I do noDon’t rRemember

This is a natural and common way to write the title in English.
これは英語のタイトルとして自然でよく使われる表現です。

My husband sometimes have as gatherings with his high school friends.

Since “husband” is singular, use “has.” “Gatherings” is plural because it happens multiple times.
「husband」は単数なので動詞は「has」が正しいです。「gatherings」は何度か行われるので複数形にします。

He told me that there i’s an old episodestory about him that is often broughtcomes up when they gaet together.

“Story” fits better than “episode.” “Get together” is a common phrase for meeting socially. “Often comes up” sounds more natural than “is often brought up.”
「episode」より「story」が適切です。「get together」は友達が集まる時のよく使う表現です。「often comes up」がより自然です。

They were teammates of an the badminton team in that high school.

Use “teammates on a team,” not “of a team.” “In that high school” is better shortened to “in high school.”
「teammates」は「on a team」と使います。「in that high school」より「in high school」の方が自然です。

One day, they drstopped in atby a Chinese restaurant after daily practice.

“Stopped by” is more natural than “dropped in at.” “Daily practice” is usually just “practice.”
「stopped by」が自然です。「daily practice」は単に「practice」と言うことが多いです。

There, my husband ordered Tianjin rice and left thehis seat for toiletto go to the restroom.

“Left his seat” is the natural way to say someone temporarily leaves their place. “Restroom” is more polite and common than “toilet.”
「left his seat」が自然な表現です。「restroom」は「toilet」よりも丁寧で一般的に使われます。

While he was away, his badmischievous friends poured much vinegar on the tablea lot of vinegar on his Tianjin rice.

“Mischievous” better describes playful but troublesome behavior than “bad.” Use “a lot of” instead of “much” with countable things. Vinegar is poured on the food, not on the table.
「mischievous」は「bad」よりも「いたずら好き」という意味で適切です。「much」より「a lot of」が自然です。酢は料理にかけます。

OnceWhen my husband came back to the table and noticed what they had done, he shouted, “No way! Damn!” He was so angry that no one had ever seen him that furious before (he is naturally calm and extremely self-controlled).

Start with “When” for the time clause. Use “no one” in negative contexts instead of “anybody.” Splitting into two sentences improves clarity.
時間を表す接続詞は「When」が自然です。否定文には「no one」を使います。文章を2つに分けるとわかりやすくなります。

However, even though they mention this irreverent episodedisrespectful story from time to time, my husband does non’t remember ithis at all.

“Disrespectful” better describes rude behavior than “irreverent.” “Story” is better than “episode” here. Use the contraction “doesn’t” for natural tone.
「disrespectful」は無礼な行動を表すのに適切です。「story」が「episode」より自然です。「doesn’t」の方が話し言葉らしいです。

When I heard this, I felt unpleasantcomfortable because ithis was a very dirty amean prank, even if you took it into account they had been childrenthough they were just kids.

“Felt uncomfortable” is a common expression for a negative feeling. “A very mean prank” sounds natural; “very dirty a prank” is incorrect. “Even though” is more natural than “even if you took it into account.”
「felt uncomfortable」が自然な表現です。「very dirty a prank」は誤りで、「a very mean prank」が適切です。「even though」の方が自然です。

I generally hate any disrespectful behaviour regardingtowards food.

“Behaviour towards food” is the more common and natural phrase.
「behaviour towards food」がよく使われる自然な表現です。

Anyway, I thought it was fortunate oflucky for him that he didn’t remember ithat himself.

“Lucky for him” is the natural phrase. “That” changes to “it” to refer to the story. “Himself” is unnecessary here.
「lucky for him」が自然な表現です。「that」は「it」に変え、「himself」は不要です。

Maybe we have a lot of “episodstories that should have had a huge impact at thate time, but in fact, now we don’t remember them at all now.”.

“Stories” is better for personal experiences. “At the time” is more concise than “at that time.” Placing “now” at the end sounds more natural.
「stories」が個人的な経験に適しています。「at the time」は「at that time」より簡潔です。「now」は文の最後に置くのが自然です。

I have ambivalent feelings for this, whether I want to recall them ormixed feelings about this — sometimes I want to remember, other times I’d rather not.

“Mixed feelings” is more common than “ambivalent feelings.” “About this” is the natural preposition. Using a dash and simpler phrasing improves clarity.
「mixed feelings」がよく使われる表現です。「about this」が自然です。ダッシュを使い、簡潔にするとわかりやすいです。

My husband sometimes (has / haves) a gathering with his high school friends.

"have" would get used for first person ("I have") or groups ("My family have"). For individuals that are not you "has" is more standard.

I'd personally use "haves" in speech, but I think that might be a specifically Irish usage.

He told me that there is an old episodestory about him that is often brought up when they gather.

I think story is more natural than episode here.

TheyMy husband and his friends were teammates ofin a badminton team in that high school.

"They" is a little unclear here, since you were just talking about your husband individually, I think it's more natural to introduce the subject again at this change.

One day, they dropped in ato a Chinese restaurant after daily practice.

Since there's a sense of movement into the Chinese restaurant, rather than the entire action happening within the Chinese restaurant, "to" is better than "at" here.

There, my husband ordered Tianjin rice and left thehis seat for toilet.

While he was away, his badmischievous friends poured much vinegar on the table on his Tianjin rice.

It can sometimes sound childish to use "bad" when there are more specific adjectives available.

I'd remove "on the table" as it sounds like they poured the vinegar directly onto the table.

Damn!”, and was so angry that anynobody had ever seen him that furious (he is naturally calm and extremely self-controlled).

When I heard this, I felt unpleasant because this was a very dirty a prank, even if you took it into account they had beenat they were children.

Anyway, I thought it was fortunate ofor him that he didn’t remember that himself.

Maybe we have a lot of “episodes that should have had a huge impact at that time, but in fact, now we don’t remember them at all”.

I have ambivalent feelings forabout this, about whether I'd want to recall them or I’d rather not.

My husband sometimes haved a gathering with his high school friends.

He told me that there is an old episodestory about him that iwas often brought up when they gathered together.

They were teammates of a badminton team in thata high school.

One day, they dropped in at a Chinese restaurant after a daily practice.

TIn there, my husband ordered Tianjin rice and left thehis seat for toilet business.

While he was away, his bad friends poured much vinegar on the table on his Tianjin rice.

However, even though they mention this irreverent episode from time to time, my husband does not remember this at all.

When I heard this, I felt unpleasant because this was a very dirty a prank, even if you took it into account they had beenare just a children.

My husband sometimes haves a gathering with his high school friends.

Here are some other, more natural ways to say this:

"My husband sometimes goes out with his high school friends."
"My husband sometimes attends (or hosts) a gathering with his high school friends."
"My husband and his high school friends get together sometimes."

He told me that there is an old episodestory about him that is often brought up when they gather.

I think you used "episode" here in a similar way to エピソード, but it's used a little differently in the English language. Better words to use here would be "story" or "incident".

They were teammates ofin a badminton team in that high school.

One day, they dropped in atby a Chinese restaurant after daily practice.

There's nothing wrong with the original sentence, this is just a bit more natural.

There, my husband ordered Tianjin rice and left thehis seat for toiletto go to the restroom.

Similar to the sentence with "episode", I think your use of toilet here comes from トイレ, but in English it would be better to say "restroom" or "washroom". You can also say "water closet", but this is very rarely used.

Also, in some countries, Tianjin rice is known as "Crab foo yong".

While he was away, his badmischievous friends poured much vinegar on the tablea lot of vinegar on his Tianjin rice.

Damn!”, and was so angry that any. Nobody had ever seen him that furious (he is naturally calm and extremely self-controlled).

When I heard this, I felt unpleasant because this was a very dirty a(or "mean-spirited") prank, even if you tookake it into account they had beenat they were children.

Maybe we have a lot of “episodes that should have had a huge impact at that time, but in fact, now we don’t remember them at all now”.

I have ambivalent feelings for this,towards this, as to whether I want to recall them or I’d rather not.

I do non’t remember

“Do not” is fine, but using contractions like “don’t” can make you sound more fluent

My husband sometimes have as gatherings with his high school friends.

He told me that there is an old episodean old story about him that is often brought up when they gatherhang out.

1. “An old episode” often refers to an episode of a TV show or a time of distress often caused by a mental condition (A depressive episode, a maniac episode, etc.). The word “story” would fit better.
2. “Gather” is correct but sounds weird, and “hang out” is more commonly used.

One day, they drstopped into eat at a Chinese restaurant after their daily practice.

1. “They dropped by works” but sounds unnatural in this context.
2. You need a possessive pronoun before “daily practice” to indicate that it is THEIR practice.

There, my husband ordered Tianjin rice and left the seat for toilet.then left to go to the restroom

1. “Left the seat for toilet” is grammatically incorrect. The correct way to say this would be “he left his seat for the toilet” but that sounds really unnatural in English. A better more natural way to say this is “he left to go to the restroom”. (And you could alternatively use “bathroom”)
2. Since he went to the bathroom after ordering rice, you should use the words “and then” to conjoin the two clause “he ordered Tianjin rice” and “he left to go to the restroom”

Note: You’ve already established that they’re in the restaurant, so there isn’t really a need to put “there” at the beginning but you can still keep it in. It just might sound a little weird

While he was away, his bad friends poured mucha lot of vinegar onto the table onand his Tianjin rice.

1. “Much” means a high amount of, but the word much doesn’t work in this context and sounds odd. Instead, you would say “a lot of”.
2. While “on the table” works, “onto the table” sounds more natural.
3. Since you’re saying they’re pouring vinegar on two things, you need to add the word “and” in between them, and you don’t need to say “on” again so we can just remove the word.

Damn!”, and was so angry that any, nobody had ever seen him that furious (he is naturally calm and extremely self-controlled).

However, even though they mention this irreverent episodestory from time to time, my husband does not remember this at all.

When I heard this, I felt unpleasantnerved because this was very dirty a prank, even if you took it into account they had been children.

1. The word “unpleasant” looks unnatural here, some other words like “unnerved” of “off put” would work better.

Anyway, I thought it was fortunate of him that he didn’t remember that himself.

1. We don’t need to use the word “himself” here, so we can take it out.

Maybe we have a lot of “episodstories that should have had a huge impact on us at that time, but in fact, now we don’t remember them at all”.

1. The phrase “in fact” and the quotation marks around the sentence look out of place, but they technically work. If it were me I would take them out though.

I have ambivalent feelings forabout this, whether I want to recall them or I’d rather not.

OPTION A: My husband sometimes have as gatherings with his high school friends.¶
OPTION B: My husband sometimes gets together with his former high school classmates.

He told me that there ismentioned an old episode about him that is often brought updiscussed when they gather.

They wereHe was team mates of a badminton team in that high schoolin his high school badminton club.

MORE POLITELY: There, my husband ordered Tianjin rice and left the seat for toilethe restroom.

注:「トイレ」という言葉はあまりにも方向性があります。 日本語の「便所」に似ています。 NOTE: The word "toilet" is too direction. It is similar to the word "benjo" in Japanese.

While he was away, his badmischievous friends poured much vinegar on the table on his Tianjin rice.

When I heard this, I felt unpleasant because this wasof very dirty a prank, even if you tooktaking it into account they had been folks were children.