the exact moment in time you realize that you are about to get royally fucked.
when you are driving down the interstate at 100 mph and a semi cuts you off. The only thing that crosses you mind is "oh shit". "oh shit" moment
"Oh Shit" moment
The point in time when you realize that what you originally thought was a good idea, was in actuality really stupid.
The point when you realize you forgot something crucial, but too late to do anything about it.
After Bob pulled the ripcord on his parachute, but it didn't open, he realized he didn't even pack a parachute for his dive.
His "Oh Shit" moment went something like this: