Not single player/story funny, but I don't think I've absolutely lost it to any game (possibly even any thing) more than Gang Beasts. Get 8 friends together for a rumble and cry laughs will be had.

One time back when we were living in an apartment with an inward courtyard facing window, my wife and I were laughing so hard a neighbour threw something at our window to get our attention so they could shout at us to keep it down. It was only 10pm on a Saturday :/