Climbing a cliff when I was five years old.
But in gaming terms, probably for completing Perfect Dark Zero on the Xbox 360. I was an early adopter of the console, and that was the best thing out on it... and that wasn't saying much.
As for PS3, it was probably something in Super Stardust HD. It was when they introduced trophies, and I got the game simply to get a trophy to my name! ALTHOUGH, they rather kindly added trophies to Burnout Paradise THE DAY AFTER I got my final license, and none of my accomplishments carried through to the trophies! I would've had an instant Platinum for that too...