oof

"Oof" is an expression when you become surprised, alarmed, shocked etc... And are about to yell "Oh Fuck" but realize there are seniors around or when u become lazy to finish the exclaim "Oh Fuck" you stop halfway and say "Oof" or "OOOFFFfff" in regret or lost hope.

Kaiz : Dude did u bring the exam paper for corrections? Because teachers gonna kill you if u aint got it.
Me: OOOOFFFF