Among other things: when you're on a street which has two lanes in one direction that, due to construction or similar, merge into one. I don't hate that, but I hate it when people wait until the latest possible time (directly in front of the construction) to merge in, despite that they saw one of these things from ten miles down the road:
I was run into another lane today by an idiot from Arizona who cut in front of me (despite my not letting him in for the very reason stated above). I leaned on my horn, but he didn't even look at me.
Well that's what I hate.

I was run into another lane today by an idiot from Arizona who cut in front of me (despite my not letting him in for the very reason stated above). I leaned on my horn, but he didn't even look at me.
Well that's what I hate.