People who sit in their cars in the middle of the lot and wait wait wait for the closest parking spot at the store. They could have easily grabbed another spot just a few feet back that would have enabled them to park and enter the store much more quickly. In their need to be as close as possible, they delay everyone else.
Something related that happened to me just this afternoon: we're backing out of our parking space at the supermarket. There are available spots all around, yet a car stops not too far behind us, waiting for our spot. The guy is too close for me to back out, so I turn and stare at him, and he finally backs up, but is still closer than I'd like. Anyway, I start backing out, but I apparently get too close for his comfort.
He actually honks his horn at me!!! Hey dumb $#!T, you started this, BACK. THE. %^&K. UP!!!