A big one for me is when people go to the grocery store and block the aisles with their carts so you can't go around and take forever. Also when people congregate in the aisles and have a freakin reunion in front of the bread and make no attempt to move when you are glaring them down.
Also people who are fake. I hate it when people only post Facebook statuses when they have something to brag about or they are just fishing for compliments.
Also people who are scatterbrained and complicate everything. An example is you are going to meet someplace and they forget the time, then they call you to change the time 2 or 3 times b/c they can't get their shite together.