Do what I do: whenever I see someone being rude, impolite, or inflammatory I point it out and ask them to behave. Like so:

http://news.ycombinator.com/item?id=2972222

When you see that someone already pointed out misbehavior (but no more than say 5 such opinions), add your own concurring opinion rather than upvoting - the offender needs to see the public opinion and they no longer see the vote count.

Also when I see a comment that does not add to discussion I downvote it.