douchenag can be defined as that nagging mother who is a total douchebag while she nags at you.
janie: mom, you're such a douchenag. get off my back, seriously.
mom: well maybe if you did the dishes every once in a while you little shit, i wouldn't act like such a douchenag.
the term shit inhalant means when you're rimming someone and they shit on your face, causing it to go up your nose, forcing you to inhale it.
john: i don't do drugs, but if i could tap that ass i'd sure take some shit inhalants.