Exactly what it says on the tin.
A moment in a video game that just about caused you to throw your controller or keyboard down so hard that you sent it through the floor.
Here's one I myself struggled with last night in fact.
Shadow of The Colossus on PS3, 3rd Colossus. But not the 3rd Colossus itself, rather the ramp and jump right before the Colossus.
I spent over a half of an hour trying this goddamn jump. Trying again and again and again. Each time I would jump....miss (either by simple miscalculation in timing, undershooting it, or forgetting that I had to hold the "R1" button to hang on) and each time I would fall down into the lake below. Swim all the way back and try again.
After I finally did it, I was so pissed that I killed the 3rd Colossus without mercy.
(But I still felt bad about it later XD )