Whether it's which direction the toilet paper is supposed to unroll, people who forget how to use coasters, or the idiots behind you who won't shut their yappers while the rest of theater is trying to enjoy "Man of Steel". There's a whole slew of things that drive us mad, drive us crazy, and push us to the point of grabbing fistfuls of our own hair and start charging angrily down the road in a naked hissy fit.
The one thing that pushes more of my buttons more than anything else though, are the lazy fools at Wal-Mart who think that a parking lot doubles as a valet service for their shopping carts. For the love of everything that is holy people, make your obese ankles walk a few extra steps and return it to the designated area a whopping ten feet away from you. Actions like this give further ammunition to the argument that mankind as a whole is decreasing its amount of intelligence.