A person of significantly low mental status, originating from douche bag. The letters are switched to signify that the person being insulted is even more retarded than a douche bag.
That guy is even more stupid than a douche bag, he's a bouche dag.
An accidental pronunciation error of the derogatory term "douche bag", usually spoken when one is extremely intoxicated and attempts to insult another person in their drunken state.
Did you see that guy's hair? What a bouchedag! Errrrr...... You know what I meant!