When someone is trying to discreetly do something on purpose to drop a hint that would be rude to say out loud, they'll say "oops" to pretend that it was accidental.
A mom enters a checkout lane with four screaming little brats.
Annoyed, the man standing behind her drops a package of condoms in the woman's cart and says, "Oops!" but he does not remove the package.
The noise mid-westerns make when they accidentally bump into someone of something
When something is going down you say oop. For example a fight.
Girl: Spills the hot PIPING hot tea.
You: Oop.
A shortened form of "and I oop" popular a vsco girl term which, when misused, gets mildly aggravating and very insensitive.
Person 1: "My cat died and I have a headache from crying so much... :("
Person 2: "Oop-"
Person 1: "..."