Justin Bieber Punches Fan in Barcelona | TMZ

... and it was all captured on camera, of course. First Bieber, then Kanye... then Bieber again. Being a celebrity is not all it's cracked up to be. Thank goodness we're not famous...

Justin Bieber did Floyd Mayweather proud, punching a guy in the face hard enough to make him bleed bad.
The Biebs was in Barcelona, driving to perform Tuesday night, when a guy ran up to the car and stuck his hand in the window to touch him. Bieber responded with a quick jab to the face.
The guy ended up a bloody mess as he and his friends reacted in shock.

TMZ