I usually call people out for being bullies and being unwilling to help newer players. They either get worse and others start calling them out, or they say they didn't realize the person was new and try to get along. Surprisingly, usually they calm down.

I did have one guy go afk and the rest of the party was furious at his behavior. But honestly, the rest of the dungeon went more smoothly after he quit "helping" us. The party couldn't argue that fact either.