A reply used to get back at an angry driver that is honking their horn at you after you have just cut them off. Originating from a shirt in which has Wile.E.Coyote is holding road runner after catching him saying "Beep, Beep your ass".
John- "Hey dude why did you cut that guy off?"
Paul- "I don't know, fuck him."
Other car- "Beep Beep."
Paul- "Ah Beep, beep your ass!"