When people walk right past the iPods in the case by the window and door, straight to the counter to ask if we have any iPods. USE YOUR EYES PEOPLE! It's not just a few people, it's every single person.
And when people use milk for cereal but they never bother to put it back in the fridge, so when I do it's usually somewhat warm.. ALSO when people use the last of the toilet paper, leave the empty on but throw the new one on the floor or on top of the empty one.. When you're in a rush to go, you don't notice nobody changed it and there's no toilet paper in the room so you have to scream for someone to save you.