One thing I believe holds well is that nasty comments are often short. Smart assholes often go for clever comments that skirt the edge of useful and obnoxious.

One thing I believe holds well is that nasty comments are often short. Smart assholes often go for clever comments that skirt the edge of useful and obnoxious. So how about a karma-moderated length minimum. New commenters (less than ~300 karma, maybe) have to post several sentences which has some chance of disincentivizing quick, brutal snark. Longer comments can still be nasty of course, but it's going to require a lot more involvement for the user while making them a bigger target for moderators.