All foul language, swear words, expletives, curses, and euphemisms (or similar words) that sound or mean the same thing as such, should be avoided, and are against the rules. Avoid using offensive words, like 'stupid'. Avoid name-calling. Avoid threats. Avoid demands. Avoid bribes. Avoid being manipulative. Avoid telling lies. Avoid the kind of sarcasm that makes someone look bad. Avoid unkind language. Avoid offending others, but more importantly, avoid being offended. Avoid slanderous speech. Avoid vulgarity. Avoid taking things personally. Avoid speaking about people's state of being sexual. Avoid racist comments. Avoid sexist comments. Avoid mockery, insults, crudeness, and lewdness. Avoid disdaining, spurning and being contemptuous. Avoid snubbing the rules. Avoid talking about sexual function/disfunction. Avoid demeaning others.
Avoid venting (as much as you can). Avoid airing grievances.
Avoid making disgruntled speculation as to whether a thread will be deleted, locked, moved, edited, etc. Avoid disgruntled speculation as to whether a post will get you banned. These things can be seen as a snub to the rules, the moderators, and/or administrators, especially if there's nothing wrong with the posts. It can be seen as demeaning the rules, moderators, and/or administrators, and as trying to incite people against them.
Don't troll (that is, don't say things with the intent to rile people up, and don't get riled up with the intent to shut someone down, nor with the intent to inspire argument).
Avoid sexual and political jokes. This even includes jokes involving sexual organs and such. Avoid referencing private body parts.
Avoid using religious language when you're not obviously being religious. Avoid acronyms that could be interpreted to include such religious language. Note: Saying "thank God" is not obviously being religious, as it's a very common expression. It will perhaps be replaced with 'thankfully' or 'I'm thankful that'. Be more explicit if you really intend to thank God, and don't do it if you don't intend it.
Avoid acronyms that include, or might seem to include, foul language.
Avoid using words relating to excrement, sex, private body parts, bodily fluids, and animals when you really aren't talking about those things. Avoid using words that describe someone with a disability out of context (e.g. lame, dumb, etc.)
Avoid attempting to force someone to reveal information. This is one way of being manipulative. For example, assuming something surprising or negative about someone so that they'll reveal their true thoughts or else be caught in your assumption. Where this is un-enforce-able, use the honor system. If it looks like you might be doing it, however, your post may be edited, deleted, or such.
If an administrator or moderator thinks your words aren't a good fit for the forum, don't argue about your integrity and the virtue of your words—those things are not the point. Don't take it personally. Your intentions, character, and interpretation of words do not justify language that the moderator/administrator has forbidden, and it's not the end of the world. Moderation is normally intended to be done in a dispassionate, objective manner. Your being upset will only make things more difficult for yourself and others. It won't help your case.
How often people use words 'in the real world' does not matter one bit to the administrator.
The spirit of the law is more important than the letter of the law, which is in part why some forbidden posts might be allowed, and in part why some posts that seem to follow the rules are not allowed.