No Twin Towers jokes, it’s too soon. 
It really doesn’t work with this kind of setup, but for your future knowledge;
I guy walks into an upstairs bar. There is only one other guy siting at the counter. The guy who walks in gets a drink and sits at the bar.
The bartender says, “hey guys I gotta go in back for a second, yell if someone comes in”, and leaves through the office door.
The guy at the bar looks at the new guy a winks. he says"You know what is cool about this bar?" The new guy asks him. The Guy at the bar says, “This block has huge updrafts from they way it was built, let me show ya”
Then the guy at the bar runs and jumps out the window before the new guy can react. He floats back up through the window, walks back to his seat and starts drinking silently.
The new guy sits there looking at the window, then at the other guy, then at the window, and back.
Suddenly he can’t stand it anymore and jumps out of the window to try.
The bartender runs back in, and looks out the window at the screaming guy on the ground with broken legs.
He looks back at the first guy at the counter and says “God you are an asshole when your drunk, Superman!”
It only works when the conversation isn’t already about Superman
Of course someone beat me to it.
I never thought it was that funny anyway.