Drifting poser kids. Skinny jeans, busted up 240s, they say they drift but can only do a random slide here and there.
Aerodynamic mods, even when functional, even when you track your car, but your car does not need them or you can't get the most out of the car without them anyway. For some reason the S2000 crowd excels in this.
I also hate the whole stretched tire/fitment scene, it makes no sense and makes cars look broken.
Slanted mufflers. I don't see the point why your Civic needs a tilted muffler, is there reasoning behind it?
Stupid trendy stickers such as "Canibeat" or whatever, you all know what I mean. 
When kids "cruise" and have their WHOLE arm out the window, as if they're trying to touch the ground. I don't know why it makes me mad, it just looks stupid. lol
People who come to car meets expecting a scene from the Fast and the Furious. I don't go to meets anymore because of it and we had a group of kids come to an Athens meet a few months ago where we threatened to call the police, they thought it was cool to rev the crap out of their cars and do a few burnouts. After telling them to stop or I was calling the police one of their "models" yelled at me "it's a car show that's what you're suppose to do!" 

 
Drift charms are for morons.
I can't stand sticker covered lips or "custom" painting. 
The whole useless roof rack thing, if you actually ride bikes then cool, but when you put a bike rack on for looks you're a damn idiot.
Diamond Racing wheels also make me mad, I don't mind the wheels, but every time I see a car with some I immediately think it's a dirt track car or a circle track car and I'm disappointed when it's a stock Civic on JDM coilovers.
Front plates also anger me, we don't need those here. Especially the people I've seen lately that drill in an older GA plate into their front bumper. LOL