1. Douchebag "alpha" male bros in their pickup trucks (usually with blue rubber testicles hanging off the back), speeding, cutting folks off, and tailgating the driver in front of them to keep anyone else from entering the lane in their vicinity.
2. Sleazy little shits in their little hondas, acuras, mazdas, whatever, modified to sound like a large insect buzzing down the road. They almost always are young, white or asian, and completely terrible drivers.
3. Young women, usually in a mid-size sedan (Passat, Camry, etc) usually with some type of "Princess" or "Queen Bitch" sticker or some such (or flower decals), driving badly, and wanting to pull up along side you for whatever reason they feel wronged by and show you they can attempt to cuss you out like a big boy.