I hate when you're waiting for an elevator and someone walks up at the same time as you, and sees you press the button, and then leans forward and presses it again anyway. By seeing me press the button and then pressing it yourself anyway, you're basically insinuating that I wasn't able to perform this action properly, something even a monkey or retarded child can do. Why don't you spit in my face and call me stupid while you're at it?
Even more infuriating is when they press it repeatedly. Tap-tap-tap-tap-tap-tap! How fucking obnoxious are these people? It's not a video game. Pressing it multiple times doesn't suddenly make the elevator travel faster. I'm not an electrician or anything, but I'm pretty confident the elevator's not going, "Oh, shit. This guy's really serious. I'd better hurry up!"
If you come to an elevator and someone's already pressed the button, do us all a favor and just relax, continue talking unnecessarily loudly into your blue tooth, and stop trying to be a hero.