One who is so totally a douchebag, that they can do nothing but act / perform every task as a douchebag; they have progressed far beyond the occasional douche lapse, and have descended into excessive, abusive douche levels; similar to an alcoholic who can not stop drinking and is dependent on alcohol, this person can not stop acting/performing as a douchebag. They are a douche-a-holic
A: I hate my boss, he's such a douche
B: Oh yeah? No one is worse than my boss, he's a douche-a-holic!
someone obviously cuts you off, turning in front of you when you have the right of way -
then the culprit proceeds to flip you the bird in the rearview mirror-