This guy walks into a bar on the top of a very tall building. He sits down, orders a huge beer, chugs it, walks over to the window, and jumps out.
Five minutes later, the guy walks into the bar again, orders another huge beer, chugs it, walks over to the window, and jumps out again.
Five minutes later, he re-appears and repeats the whole thing.
About half an hour later, another guy at the bar stops the first guy and says, "hey, how the heck are you doing that?!"
The first guy responds, "oh, it's really simple physics. When you chug the beer, it makes you all warm inside and since warm air rises, if you just hold your breath you become lighter than air and float down to the sidewalk."
"WOW!" exclaims the second man, "I gotta try that!" So he orders a huge beer, chugs it, goes over to the window, jumps out, and splats on the sidewalk below.
The bartender looks over to the first man and says, "Superman, you're an asshole when you're drunk."