Duffsex is where erectile dysfunction, performance anxiety or alcohol intoxication leads to the disappointing premature discontinuation of intercourse without climax by either participant.
guy1: dude, did u hear hadi got laid last night? with this bear fit irish chick innit!
guy2: yea but it was duffsex... how embarrasing. shame about the bird too, she's zhaofit.
guy1: no way! is he gay?
guy2: no think he was just too wasted innit and such.
guy1: well, at least he didn't have to pay this time.