a form of cuddling.
when i female duck has ducklings, she keeps them under her wings/breast.
only instead of a duck, it's when a girl lays, or cuddles, more or less on top of a guy rather than beside him.
"oh after sex last night we were duddling... until he couldn't breathe."
really meaning "you're fucked," but in a cute, t9-savvy way that's being brought into actual conversations the way "lol" is now.
Buddy: crap man, my girlfriend caught me cheating on her.
Guy: you're ducked, dude.
Friend: yeah, totally ducked.