Tex in Red vs. Blue gets this moment when Donut lobs a plasma grenade over an incredible distance, square into the cockpit of the tank she was driving.
Everyone is one the receiving end of this at least once, although their reaction is less "oh crap" and more "son of a bitch!"
In Recreation Episode 12, Donut is cleaning up Blue Base when he's approached by what he thinks is a new Blue soldier (it's actually the previous season's Big Bad, Meta.) Donut, being Donut, tries to strike up a friendly conversation with it, evading its attempts to kill him by near misses. Simmons then arrives, Donut tells him about the new soldier, which leads to this:
Simmons: "What? They sent another team member? Why would they do that? That doesn’t make any sense- (sees that it's Meta)OH, FUCK!(starts to run away) Welcometotheneighborhood, seeyoulater!
When The Meta attaches the memory unit containing the recently captured Tex to his armor
The Meta is the living personification of this trope he even has his own Theme music which makes the Imperial March Jaws theme and Psycho Strings look tame in comparison
The Demented Cartoon Movie: An underwater diver recites the trope by name upon realizing that the "Bubble Fish" he has been tracking is actually Zeeky H. Bomb.
Happy Tree Friends is a total definition of this trope. Nearly every episode has it's Oh Crap moments (save for just a few). In the fanimation "All Work and No Belay", before Lumpy falls and rolls into a big snowball, he notices what will happen and holds up a sign saying "HELP?".
