Car horns. Or rather the obnoxious use of them. Some days I just want to take to that relatively pristine yellow taxi body with a baseball bat. Worse, worse, worse than unnecessary horn honking is when I'm getting out of/into a cab and the person in the car behind starts honking because the taxi pulled up. Well, duh! That's what cabs do. I have to give those people an absolute mouthful before I can get on with my day.