What are some of the worthwhile communities?
Standard disclaimer applies about 4chan. If you're thin-skinned, you may find it not worth the trouble. Just don't engage with the trolls and you'll be fine.
It's funny, when a community pretends to be stupid for the funnies, it's not too soon before the actual stupid people move in.
The biggest problem I see on /diy/ is questionable humor, sort of like how blue collar occupations used to haze the apprentices a bit, you'll see the most ridiculous / comical suggestions sometimes.