When someone is commiting an act of douchebaggery and the people around him/her make a "d" shape with their hands and say "D um' up!... DOUCHE!"
Often followed by the douchebag's own form of retaliation (example: "That's what she said", "Screw you", ect.)
Sometimes the "...DOUCHE" ending can be subtracted, leaving the douchebag confused and angry.
Douche um' up.
Douchebag- Jeez. You guys are so boring. blah blah blah.
Anti-douchebags- D um' up! DOUCHE!
Douchebag- Wow, you guys are faggots. blah blah blah.
Anti-douchebags- *walk away in a pack*
Douchebad- You guys are such nerds! blah blah blah.