what are some good openings with a trap to play *against* beginners? For instance, I consider the Queen's Gambit to be such an opening. Most beginners playing black would accept the gambit, and try to defend their pawn too, leading to inferior lines for black.

Any others?
There is none. You should play the openings where you are stronger, and you should play normally as if you were facing a strong opponent, because if you let your opponent get some kind of messy position you are risking losing yourself.

All I can say is to play good moves, sooner or later your opponent will blunder something.