"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