Baltimore Trebuchet

The act of going up onto a roof with a cinder block, facing away from the edge - then picking up the cinder block with both hands and flinging it backwards over your head in the same way a catapult would, tossing the cinder block onto the street below. The perceived purpose of the Baltimore Trebuchet is to hit the cars parked in the street below.

"Yo I heard Joey got arrested last night, what happened?"
"Ah, he got super drunk and decided to start a game of Baltimore Trebuchet."
"Damn, I knew that guy was a dumbass."