People who amble about with no courtesy to others, as though they were the only ones on the planet.

I've got about ten of them related to grocery shopping alone. Everything from people not paying attention in the parking lot, to people hogging the aisles chatting it up while you are trying to get around them, to the people with fistfuls of coupons that want to argue about the cost of every item. Then the people who get up to the checkout and forget that they needed something else, so they hold up the line while they run around the store.

The slow walkers drives me nuts, too. Usually they are busy texting and walking, or reading an e-reader and walking. I just want to take it out of their hands and throw it.