It's kinda funny, I had a moment recently that SHOULD have been a FFFFUUUU moment, but I just found it too hilarious to get angry.
I was playing Left 4 Dead 2, and it was the last part of a campaign level. We were on the rooftops waiting for a chopper to appear. It came, and everyone except me was close to it, so they got right in.
I had just been revived a few times, so if I got knocked down again, I was dead. I headed for the chopper, just barely scraped past a few zombies, got to the platform I needed to to board the chopper... and one of my teammates shot me in the head with a sniper rifle. He didn't feel like waiting for me to get there, so just "boom" headshot. I didn't even realize what had happened until the other two asked him why he did that, when I was almost there.
I should have been angry... but I just found it really funny.
Anyways, probably my biggest FFFFFFUUUU moment is WAAAY back in Pokemon Red. I was at the Elite Four, and I had brought the game to my friend's house to show him. My team still wasn't strong enough to beat them, but I figured I could level them up and take down the E4 the next day.
Little did I know that at some point, my friend's brother got ahold of my game, started playing, entered the Elite Four chamber, and saved. As you know, once you enter, you can't leave the Elite Four chamber. And stupid me, I didn't know that if you lost a match, you only get sent back to the Pokemon Center, I thought it meant Game Over.
After beating the hell out of my friend's brother for doing that, I restarted my game... only to find out a week later that I could have just lost and tried again. FFFUUUUU....