A prank involving someones head at your crotch level. You stand next to the victim and either quietly or loudly (your preference) start humming the Superman theme. When everyone turns to look at you, it will appear that the victim is performing oral sex on you because they're looking at you also.
"...And then Rob supermanned Greg, and for the rest of the night, easy laughs were had just by humming the superman theme around Greg. Never pass up the opportunity to 'superman' someone."