Rule 8 briefly
What gets you banned (most common and general reasons):
-Posting pepes, wojacks, discord or reddit type memes and their meme macros, media that is obviously from cancerous places (You do know what I mean)
-Using their lingo in any capacity, unless further heavily justifying context is present (I guess)
-Reposting tiktoks, or other mainstream things if too obnoxious (I think)
-Using greentext for anything other than quoting
-Heavily subverting Heyuri culture

What could get your post autosaged, locked or deleted:
-Politics, there has not been many instances where heyurizens post politics anyway.
-I don't know, its quite rare.

What can make heyurizens repulsed by you:
-Every heyurizen can smell you are a foreigner unless you dont assimilate (same case is for every chan if you don't lurk enough though).
-Posting with a file name obviously stating its origin from things like facebook
-(We know its origin if the jpg is blurry)

What unrelated to rule 8 gets you banned:
-Check them, dubs, trips etc.
-Flame wars and ragebaits
-CP
-Being too serious with no necessity, usually related to rage (I think)
-Vtubers (I assume)

Check rules to make sure, I only cherrypicked some of them.

Replying directly to OP in threads used to be a way to get banned, now it seems nobody gets banned for it.

A healthy advice is to lurk and look at past threads to have an understanding of what is generally acceptable.
I don't want to sound harsh on what is good and what not because Heyuri seems to be fine with pretty much anything, but please avoid the most obvious ones.
Don't induce annoyance in oldfriends the same way I do not wish to do this to newfriends.

Post tricks
https://heyuri.net/index.php?p=faq

Put this in "name" field:
noko - default, makes you return to the thread instead of main page
sage - makes thread not receive a bump
nokosage - sage and noko combined
flag - displays a flag depending on your IP
fortune - picks one fortune for you

If you make the thread:
displayip - displays IP range of all posters like 123.123.*.*

I think there are more but I don't use more and so I don't remember.

There are wordfilters for PENIS, VAGINA and partybus or partyvan. I don't know of others.

About formatting posts, you use BBCodes with two square brackets, they work like HTML tags.
You can format mindlessly using the BBCode option while typing.
Make sure you tick the box before trying to "Add" it, it won't work otherwise!
You can type them out manually too.
There are tags for posting ASCII/SJIS art without breaking and making parts of post scrollable like mine.
I am not sure about the art tag, but scroll tag is just "scroll" and remember to end it with "/scroll", same for all BBCodes.
Using big text is not usually banned but please don't over do it.

Culture and History and Anything
Events and customs that I personally remember, not in a particular order.

1. Heyurizens made music albums that you could order. I think that the order site still works but albums have been wiped from internetarchive. Can anyone reupload or link to them? I'm interested in original files. There were two albums.
2. There was sort of a craze for Chen from touhou for some time. There are 3 heyurizens proven to have a Chen costume. Later Dejiko stole the title of the most popular catgirl (Opinion).
3. We hold (I think) monthly anime streams, anyone can join. It is heavily announced each time in advance. We do not seem to play games together much besides CGI. Heyuri also has a Steam group and a MAL group.
4. Tripfagging seems to be alright, but naturally you can associate a tripfag with bad posts if you find them annoying.
5. We hold bunkasai each year where heyurizens show off what they do and we play together, tanabata was celebrated last year, and we do collages of christmas with our 2d wives.
6. Mascot of Heyuri is Heyuri-tan. wiki.heyuri.net/index.php?title=heyuri-tan and she is a hybrid of multiple moe characters.
7. The heyuri spray banner was made by a kid in wisconsin or something, probably made in an abandoned factory
8. There was a craze for LOL PENIS and LOLI PENIS, no idea.
9. Heyuri tried to make up a word for a german youth word vote, "lolicious".
10. Heyuri played minecraft, "Age of Autism" server, and I still have the world save
11. We had a desktop thread, 90% of heyuri is on linux it seems
12. Azumanga was very popular for a long time, now it seems is not as frequently posted or talked about as it used to be
13. Source code for Heyuri is on github.
14. Heyuri in general prefers older things (except for lolis).
15. It is recommended to be familiar with japanese and japanese stuff for Heyuri.

Personal thoughts
1. There are people who get angry sometimes and act angry.
You either joyously respond to an angry poster or not respond at all.
Nobody benefits from cultivating anger.
If you made an angry post be sure we forgive you.
We all make terrible posts from time to time.

2. Old times always feel better because you had more time to tolerate past threads and past movements unlike "new bad times" that have thread and movements you have not started tolerating yet.
Being a newb is like childhood in a way, you feel the charm of a wonderful world that you do not understand - you enjoy it instead of having mastered it - and I think it contributes to favoring "old days" where you did not realize there are bad things and had too little information to compare them to in order to determine they are bad. And memory is selective.

3. There are newfriends and there will always be.
It is a duty of oldfriends to assimilate newfriends.
If newfriends don't assimilate it can be usually be attributed to oldfriends failing at passing down culture.
Steady influx of new users is a survival condition for every site and there is a peak in every society whose greatness must be watered down by newbs for survival.
We either do good on our part as teachers and friends or we fall.
Newbs are annoying but that is natural, nothing we can do besides teaching.
In worst cases we can only hope that mods ban those who grossly demonstrate they are not interested in participation like rule breaking.

Threads
Threads I liked
>>127943 - lucky star rape fantasy
>>123266 - chiyo posted
>>122926 - triforce

Silly threads
>>127628 - happy
>>126290 - gangsta rap
>>125541 - zundamon gets murdered by a heyurizen
>>124346 - flag
>>124057 - youtube
>>120683 - rumia is hungry
>>120062 - paranormal
>>119566 - konata stripping
>>110314 - tanabata
>>110692 - heyuri having japan at home
>>128419 - christmas

I picked them somewhat randomly, there is much more to explore