I remember my childhood friend Max and I got really mad at each other for like a day or two after playing Metal Gear Solid: VR Missions all night. Nothing major, but man were we angry with each other over something stupid.
I should say that we were both about 11 or so.
Come check out my music at www.last.fm/music/tyler+hellner PSN ID: Senor_Rub_a_Dub
Actually yes. A friend and I were playing SF3S online against each other. He'd been playing the game for years and I just picked it up; but I'm pretty good at action and fighters in general. After three matches I started a win streak which in stead turned into a gigantisch slaughter for a long time in which I perfected him to no end. Eventually he disconnected mid-match and gave me an entire rant online. We never spoke again, even in real life.
We sometimes get into verbal fights, usually just one of my friends, who constantly tries to glitch or get himself into the unbeatable position. But I've never come close to actually losing a friend over playing a game.
"I have two rules I follow. The first, never kill someone without a reason. The second, you can always find a reason to kill someone." - Saren