Despite going through most of it feeling "is this supposed to be funny? How is this funny?" there was one moment in Borderlands 2 that nearly made me fall off my chair laughing. It's when you meet the guy who wants to face a gun (if you've done this quest you know what I mean).

Saints Row 3 during the insurance fraud side activity.

Probably Psychonauts...

The last game that made me laugh was No Time to Explain (last week or so):

"ARRGH!! MY INSIDES AND MY OUTSIDES ARE IN PAIN!!!..." :D

I can see why you've not got time to explain but maybe you should seek medical attention rather than posting on this whimsical topic?

The last game I played that made me laugh out loud really hard was Stick It To The Man!

There are lots of Tim Schafer-y moments in that game, but that "final" countdown by The Mother in the space station was awesome-sauce. "Three. Two. One. Zero respect is what I get, seriously?!"

The game's writer also likes to make a whole lot of poop jokes, which is fine by me.

The Book on Unwritten Tales has some brilliant parodies about RPG games.

I can't pin this down to any specific game ... but I remember having a giggling fit after daring to pick the multiple-choice dialogs most inappropriate answer.

Recently hired the mercenary Steroid in JA2. When he finds a booby trap he exclaims: "Wait, here is a Boob trap!" in a thick Arnold Schwarzenegger voice :D

Within the past few days, playing Risen. The main character has a dry wit. His delivery is typically very good, especially when dealing with residents of the swamp camp.

Do you see anybody getting wealthy around here?
Not unless the local currency is mud.

NOLF 2 and listening to the young female ninja talk about how her mother just doesn't understand the dress-code for modern female ninjas - that cracks me up every time.

The Last of Us launched my sides into the orbit.

The Book of Unwritten Tales had a few moments when I actually laughed out loud. It makes jokes on RPG clichés and on the Lord of the Rings. Also some original jokes were pretty good too.