Playing Bioshock with a friend. We accidentally hit a big daddy we could ill afford to fight, so after a brief whirlwind of gunfire, explosions and "Oh shit!", we ran out into an open area to recoup and escape, at which point:
"Oh SHIT! There's TWO OF THEM!"
When in L4D all pretence had been abandoned and the group had dissolved. Two AIs were stuck in a room surrounded by zombies, I'd died and my good friend had decided to leg it. It was in the sewers on No Mercy, so imagine his surprise when he saw a tank in the dark. He ran down a thin tunnel and it got stuck. Later on the same game, we were badly mauled and clambering out of the sewers. My friend stuck his head out of the sewer and weas promptly swarmed by zombies. We found that, provided he stayed on the ladder, they couldn't get down but they could hit him. Eventually he was beaten into submission and a STREAM of zombies flew out of the entrance. Like, you couldn't see the ladder for zombies.
On Gears of War we were in the arboretum and my friend said "I know this game. Something big'll come through that wall there". A beserker promptly smashed through a door to the right of it. After some buggering about, we got on the other side of the wall and sighed collectively. Then the beserker smashed right through our side of the wall and was greeted by a hail of lead and bad language.
We survived all these, by the way.