Brad owning 1UP.com during a live stream of the StarCraft II multiplayer beta. And then Bob Colayco shows up...
During their StarCraft II TNT there was a particularly tense fight against a Zerg player who used lots of distraction tactics. The match itself may have been fairly typical but the commentary from the rest of the crew made every move seem awesome, because none of them knew what was going on and started borrowing terms from other competitive video games.
Playing a few rounds of Team Fortress 2 during the Happy Hour one week with Robin, aka Robin Walker, who created the damn game. Even better, one of the guys was playing Medic on BLU and proceeded to heal Robin (who was playing Soldier) during the setup period, and Robin saluted him and said thanks.
Dan Ryckert finally beats Mike Tyson in Mike Tyson's Punch-Out!! by KO after trying and failing for the last twenty-five years. What makes it even more awesome/hilarious is that this was the first video of a planned series where he'd try for half an hour every day until he succeeded.