To Rev the crowd is an action that is preformed at a concert by the lead singer (most likely).
To get the crowd at a show more rowdy, a band member may rev the crowd by placing both hands in the air above his head (like riding a chopper bike) and like you would do on a motorcycle to rev the engine, you twist your hand up and down.
To chop the meat is an action that takes place during a concert or while listening to music.
Place your inside hand on the subject's arm for starters. Begin the chopping motion on the subject's arm (not to hard)with your outside hand just below your "holding hand". Now move your "chopper" down the subject's arm slowly while chopping at a moderate to fast pace (keeping with the beat of the music).