Catching up on some forum reading...

I dislike:

People who seem to lack the understanding of a "zipper" concept in traffic. And those who think Yield means the guy already on the highway always has the duty to accommodate merging traffic. I actually had some lady trying to road rage me because I let 5 people on and not her... Yes, I'm nice but not all day long.

Lack of common courtesy. Even a small nod is enough to convey respect.

People who eat and talk while on the phone or voice chat. I do not want to hear you eat in surround sound.