Idiot Number Seven : Arkansas: Seems this guy wanted some beer pretty badly. He decided that he'd just throw a cinder block through a liquor store window, grab some booze, and run. So he lifted the cinder block and heaved it over his head at the window. The cinder block bounced back knocking him unconscious. It seems the liquor store window was made of Plexi-Glass. The whole event was caught on videotape. Yep, here's your sign.
I've seen a video of two guys trying to break into someplace. Guy #1 hurls a brick, which bounces and knocks out guy #2. Guy #1 picks up brick again, throws it, and knocks himself out.