For example, words like breast, ass, or other slang terms for body parts may not be uncommon on my site.. due to user submitted content, so I'm afraid that this might cause trouble with Google. Would adding the weight=ignore thing to the possibly offending text be a good safeguard for this? Or would those words still have an effect on adsense? Or should i just not worry about this too much?
I wouldn't worry about it until you start seeing PSA's on pages - you wont get banned unless that's ALL your site has, but those 'stop' words might get you PSA's on those particular pages. Since i dont want to worry about it, i've added word-filters to my site to replace the 'naughty' words with 'happy' words..
Just be careful enough to not approve every content. That's why a moderating team is good. You should worry about it. Not for Google, but for your own visitors FIRST.
As Tearabite said, dont worry until all you get are PSAs, ask other people if they see PSAs too just in case.
I don't think it's those stop-words you actually need to worry about, so much as words and phrases about clicking on ads. There is some possibility that these can get you auto-banned. What you can do is have some fun with word filters. You could replace the offensive words with family-friendly alternatives, or just with ****'s. And you could do likewise with anything to do with invitations to click on ads. Google obviously hasn't released a list of words and phrases that you must avoid, but I'm sure you can think of at least a dozen examples that would be worth censoring.