Wikipedia:Offensive material
One of Wikipedia's rules to consider:
Avoid "foul language" (words that could be considered offensive by typical Wikipedia readers), but not at the expense of accuracy. We strive to create a serious encyclopedia with brilliant prose.
Avoid foul language in particular in usernames: see the offensive username policy. Most participants feel that tolerating offensive user names has few if any benefits, but can turn contributors away who see them in the list of recent changes or elsewhere, and this outweighs freedom of expression.
There is rarely any need to use profanity in article titles. Since Wikipedia is not a dictionary, there is no need for definitions of profane expressions or euphemisms for them.
Well written articles should not, on the whole, need to use profanity. However, it may be warranted in some cases: articles specifically about profanity are an example, and when mentioning someone else's use of it, you should go ahead and be accurate. If you are including some famous person's exact quote, don't censor -- tell us what he actually said, as long as the quote itself is relevant to the article. There's no point in turning an instance of "fuck" into "f***" or "the f word"; if you wish to do that you should paraphrase rather than quoting.
While welcoming contributions of almost all kinds, Wikipedia encourages the use of a professional 'tone of voice'.