A combination of the words dumbass and ambassador.
Refers to people that speak, act or behave in such a moronic manner, that one might think they were to represent all stupid morons in this world.
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.