For me, the ones to watch out for is any car or truck containing two or more young guys. They're the ones that throw things at me, and I can just imagine that every time, it is preceded by: "Hey, watch this!" If they're well behaved enough not to try to clip me or throw things at me, they can't refrain from shouting something out the window.
As someone posted earlier, it is usually an afterthought. I can't see them coming, but I can tell the demographic as they pass by.
This week, as I was riding home, some guys shouted out the window at me: "WOOOOOO!" I caught up to them at the light, pulled up next to them, and gave them the: "What was THAT all about?" look. One of them timidly replied: "Nice lights." Somehow, they lose their courage when they are no longer anonymous or going 40 mph faster than us.