What's a specific pet-peeve of yours?

I'm looking for something that's really grinding your gears. Something that just makes you explode internally. We all must have something that annoys us more than it really should or at least, it's something that would be totally not an issue to about 99.9% of people in the world. For me, the one thing that really gets me is when I go shopping and I see items that are left in random places for no obvious reason. Like why am I seeing a pint of milk in the booze aisle? Decisions were made there it seems. Just really irritates me! 
What about you?