Oh crap (ConceptTopic, 4)
From Compile Worlds
Oh crap is an expression that is usually spoken when some one is in trouble or suddenly realizes something. Most of the time, it is impulsively spoken, since usually there is little time to prevent it from leaking out of your mouth. Sometimes, it is also spoken when someone realizes they forgot about something important, such as forgetting to write this page after red-linking it on the Zeeky words page.
A variation of "Oh crap" is "Oh shit,", which is usually reserved for either more vulgar people or for more serious situations. Yes, this includes being in deep shit.
"Oh crap" has slowly made it's way into the hierarchy of interjections over time, joining the ranks of even more common phrases like "Aw yeah."