The essence of humor is surprise. Some things are funny because we don't expect them at all, and others because we expect them but have no idea when, where or how they will happen; the release of tension when it does occur makes us laugh. It is the surprise that makes humor different from typical videogames rewards. But the game experience isn't simply imposed on players by the writers, programmers and designers; it is created by the interaction of the player and the game. Nothing is more surprising than people, so humor can crop up at any time during gameplay.
While developers work hard to write funny dialog and situations into a game just like novelists or screenwriters, there is a tremendous potential for humor inherent in the very nature of gaming. Players always experiment with games, using them in ways the developer never intended or expected. The ESRB now warns players their "Game Experience May Change During Online Play" for virtually any game with an online multiplayer component, but this caveat is true for every game. And the more choices a game gives the player, the truer this becomes. Emergent humor, whether it be an accident of play or deliberate goofing off, is the funny stuff that happens when you aren't really expecting it. Just like a coin is not intended to be a screwdriver but does a pretty good job of it in a pinch, so too can Counter-Strike be a comedy goldmine in the right hands.
My first computer ran at 10Mhz, and I thought it was pretty fast. Games of that era did not have much flexibility built into them, but they had enough for that most primitive form of humor: the spectacular failure. Players lose all the time; the anticipation of failure and the struggle to avoid it is the most fundamental dynamic of play. However, while we all know that we can lose, we rarely imagine ourselves losing in the worst possible way. It surprises us when it happens, and the shock makes us laugh. My first experience of this sort in a videogame was while playing a version of Spacewar, a two-player space ship combat game. In Spacewar, two ships with weapons, shields, cloaking devices and a random-drop hyperdrive fight around a planet. I had managed to reduce my opponent's shields to critical levels; victory was within my grasp! However, in my excitement, I pushed the hyperdrive button instead of firing a weapon. The drive dutifully engaged and teleported me straight into the planet, killing me instantly. My opponent and I both laughed for so long our respawned ships were pulled by gravity into the planet and destroyed again. This was to set the stage for much more laughter at my own misfortune in the years to come.