A combination of the words: Stupid and Douchebag. A more efficient way to call someone really stupid who is also acting like a douchebag at the same time. While it may seem redundant, Stuchebag is used when "douchebag" alone does not convey the level of douchebaggery going on.
The act of being a stuchebag is: Stuchebaggery. As in: the amount of stuchebaggery being displayed by that kid is astounding. Somebody should punch him in his pussy.
Did you see what Jared did at the company picnic? He was not only completely shitfaced and making a fool of himself in front of the little kids trying eat their lunch.... but he was hitting on the CEO's wife while the CEO was standing there. What a complete stuchebag!