In a WoW vein, again, in the next patch (1.12) they’re adding warlock minion voice emotes. Your imp, voidwalker, succubus, doomguard, etc. will actually talk.
Now, understand that to summon a doomguard requires a sacrifice…one of the group that summons him has to die. Well, one of the new doomguard “summon” voiceclips is, “What happened to your friend?”
Samurai Showdown 4
And ONLY WoW 'locks are going to even chuckle at my last post…
Nope, this mage think’s it’s funny too. Good thing Zylok never summons a doomguard though, because if I heard that after I got sacrificed…well, lets just say one of the requirements to get into the Horde side of our guild is to provide a recipe for cooking gnome meat.
The conversations between the guards in No One Lives Forever (or was it part 2?) were very funny. There was also a guy selling monkeys and the conversation went something like this:
“You look like you need a monkey.”
“Excuse me?”
“I have a very fine monkey for you. Only twenty dollars, American.”
“Sorry, but I don’t want a monkey.”
“What did you say?”
“I said I don’t want a monkey.”
“Why not?!”
“Because I don’t like monkeys!! Now get that filthy beast away from me!”
“Are you insulting my monkey?!”
Har! You reminded me of another one…
Raz: So, is this the part where I listen to a long lecture about how dangerous it is to lose control of one’s own mind before you give me my merit badge?
Sasha: No. Here’s your badge. Let us never speak of this again.
And there were the “secret agents” who wandered around in Boyd’s mind, pretending to be people they obviously were not, carrying around various objects as a “disguise”. For example: to get into the cemetary, you need to disguise yourself as a grieving widow. So, like the other secret agents, you need to be carrying a flower. If you speak to an agent, you will say, “I am a grieving widow,” and the agent will respond in a husky male voice, “I am your sister in grief.”
One thing I found interesting about the game was the hidden traumas of the various characters.
[spoiler]Through the magic of ViewMaster, we learn that Sasha’s mother died while he was still a baby, and the loss apparently still haunts him. And when he reads his father’s mind to learn about his mother, he apparently sees a bit more than he’d like to, which compounds the trauma, leading him to run away from the family business and hate tacky lamps of the sort Dad made forevermore.
And then there’s Milla. Hidden in her psyche is a “nightmare room” filled with whispering ghosts from her past: apparently, she was a nurse or nun or something of the like at an orphanage. One day the orphanage burned down while she was away, and the deaths of the children haunt her mightily. That is one creepy room, what with the locked-up nightmares whispering “milla, why did you let us die” and “we’re burning, milla” over and over. For a woman whose entire psyche is a combination pinball machine and dance club, that’s some heavy stuff right there.[/spoiler]
And hidden traumas like those above are really just background; they tell you about the characters, but they’re not a vital part of the game. Just part of the rich tapestry that is the story.
I second Psyconauts…
Also I thought this passage (Voiced by Happy Mondays legend Sean Ryder) from GTA San Andreas was one of the funniest I’ve heard in a computer game (though could just be my sense of humour)… Spoiler used cos of slightly adult dialog 
PAUL - You shouldn’t be choking the gecko in the first place! Remember what happened at that gig in Hamburg?!
MACCER (Voiced by Happy Mondays legend Sean Ryder) - That groupie loved it!
PAUL - That wasn’t a groupie, that was a roadie!
MACCER - But she had great t1ts.
PAUL - MAN t1ts! They were MAN T1TS!
There was a map in Heroes of Might and Magic II in which you play a necromancer who travels across the countryside building up an army. The way you do it is to slaughter thousands of peasants and raise them as skeletons. This utterly horrific strategy, combined with the game’s cartoonish graphics, just cracked me up for some reason.
THe funniest thing I’ve ever seen in a game, though, was the Cow Level in Diablo II. Especially the sound effects.
Daniel
I love the indignant cry when they die. MOO!
The Dynasty Warriors series (all of 'em!) are a riot and a half, especially if you know the original source material (although, occasionally, it does enrage me to the point of spitting blood on some of the character designs).
My favorite story modes are Zhang He (who’s such a fruitcake he makes the Kids in the Hall look straight), Zhang Jiao (his dub voice actually made me laugh instead of cringe), and Meng Huo (two words: War Elephants).
The vegetarian cannibals in Curse of Monkey island are fantastic. They worship a volcano that suffers from gastric reflux, so they have to be careful what “veggies” they give him. Guybrush throws a hot pepper in the volcano and causes an eruption.
He also disguises himself by carving a face into a huge chunk of tofu and wearing it on his head.
Also, the end of Monkey Isand 2 is fantastic. It’s revealed that LeChuck, the main villain, is actually Guybrush’s brother.
Guybrush says, “Just tell me why? Why do you chase me around trying to kill me? Why did you raise up an army of undead pirates? Why? Why? Why?”
LeChuck says, “Well, remember when we were little? One time, I was making this wall out of blocks. Remember when you came in and knocked it over and then laughed at me?”
Guybrush says, “No. I don’t remember that.”
LeChuck says, “Oh. Nevermind then.”
Fantastic!
I had something similar happen to me in one mission. I was flying in a TIE fighter fighting a single A-wing. Frankly, the TIE is no match for an A-Wing; the A-Wing has shields and is too damn fast for a TIE fighter to have much of a hope. I was certain that I was never going to be able to take down the A-wing when all of a sudden it flew right into a space station. boom, mission completed.
“Mind if I drive?”
“Not if you don’t mind me clutching at the dashboard and screaming like a cheerleader.”
-Sam and Max Hit the Road
One of the things I liked about Destroy All Humans! was the fact that you could read people’s minds. Led to some great fun with just running around in disguise and listening to the comments:
“I love my mother. A lot. Is that so wrong?” -Town Geek
“Bill of Rights? Who needs a Bill of Rights? I’m Bill, and I’m Right!” -Cop
“One drink at breakfast, another at lunch, and if I’m lucky, I won’t even remember dinner!” -Housewife
Besides, you have to love a game that features the anal probe as a weapon and has a level with Exploding Radioactive Zombie Cows. A little short, but fun.
There’s also some good lines in Stubbs the Zombie in Rebel Without a Pulse. I like the parody of the opening speech in Patton. There’s also a part with a hillbilly trying to put the moves on a sheep. If you kill the hillbilly, you hear the sheep say “From this day forward, sheep and zombies shall be friends!”
City of Heros/ Villains has plenty of funny dialogue. For example, “The Bad Protest is the one with all the head injuries” and “No, ‘Non-violent protest’ does not mean ‘knives only’ !” from the Luddites. I also remember coming across some guy in CoV who had been given the Mafia-style bit where his feet are stuck in a cement-filled tub; he was hopping like mad along the sidewalk.
Final Fantasy X-2…Yuna’s a Gunner, Yuffie’s a Thief. I can’t remember what Paine was, but it’s unimportant.
They’d just won a battle, where Yuffie had advanced through the enemies to collide with Yuna.
So, Yuffie ended up straddling Yuna’s leg, doing her little pelvic thrust victory dance.
OK, let’s not be delicate…Yuffie was humping Yuna’s leg.
Let’s just say, it entertained me.
I think—though I’m far from sure—it was the one where you had to make your way to the college campus, with the duplicator ray mounted on the roof shooting at people. In any case, it was during the daytime, in the mostly normal city (i.e., not when it’s frozen-over, taken over by plants, or transported through time), and I’m pretty sure it wasn’t after about halfway-through the game. It would have either been on “normal” or “easy” difficulty.
Not much to go on, I’m afraid. 
I had a good one recently playing Vice City although it may have been a glitch in the game.
I was escorting Cortez out of town on his big boat and the French attack. I had tons and tons of weapons by this point so I wasn’t especially worried. The first wave of 8 men didn’t even make it away from the dock before I blew all the boats up. The second wave of boats got off about one fusillade before I sunk or killed them all. Then the helicopters showed up. I took my M-16 and started bucking. For no readily apparent reason it cut through the helicopter like it was made out of cheese and all four guys fell out of it dead. But the helicopter still had momentum and it was headed right for me. By some miracle it soft landed on the back deck of the boat. Right after it landed another helicopter showed up and I did the exact same thing, blasting all the guys out and causing the helicopter to land… right on top of the other one! For some reason it bounced off the rotors and a lone survivor jumped out right in front of me, which was the worst place he could have went. But while I was dispatching him, the empty helicopter took off again! I’m pretty sure it flew off and crashed. It was the weirdest thing I’ve even seen in a video game.
The dialog of the grumpy stormtroopers in “Star Wars: Jedi Outcast.”
Those guys were hilarious.
I’ve never once played WoW and I thought it was hilarious.