GTA:SA was a great game for just going mental. My cousin and I used to turn on co-op and just go crazy with the cheats any time we just wanted the lulz. I think one of the funniest moments was when we got a helicopter, flew out of SA into SF (which immediately set the cops after us), we made it to the city before they shot us down, and so we skydived down. I pulled the ripcord on my parachute too early, so I got shot out of mid-air, and landed in the middle of the street. XD My cousin spawned a jetpack and flew away but basically crashed right into a police helicopter, which promptly blew him up.
As far as games with writing that was hilarious on its own, Abe's Oddworld & Abe's Exodus both had me laughing hysterically. MediEvil as well. And, even though its moments were pretty cringe-worthy, sometimes FFX-2 cracked me up - it eventually grew on me. Most of all, Portal though. There were moments in that game where I died because I was laughing too hard at GLaDOS.
As far as games with writing that was hilarious on its own, Abe's Oddworld & Abe's Exodus both had me laughing hysterically. MediEvil as well. And, even though its moments were pretty cringe-worthy, sometimes FFX-2 cracked me up - it eventually grew on me. Most of all, Portal though. There were moments in that game where I died because I was laughing too hard at GLaDOS.