Some coop games, like Battleblock Theater or Magicka, were definitely the most funny for me, with all the dumb stuff you can do, fuck with your friends, etc. but those depend on the people you play with. With friends, every game can become super funny though, even more serious stuff.

As for single player, the ones I remember the most were Donut County and maybe the Frog Detective games, those had some really funny moments and writing.