It really depends on your sense of humor, but in the movie Saving Private Ryan there is a scene shortly before the final battle begins in which a record is playing and Ben Afflec's character is retelling a story from his youth. That scene is a gem, especially considering how serious the tone of the movie is.
In the 40 y/o virgin when he is driving back from the first party and the girl is driving all over the street and then she goes and pukes on him . . . monumentally funny!
Pineapple Express. The scene where Seth Rogen is kind of attacked by a butterfly when they're lost in the woods. It doesn't sound very funny but my friend and i were laughing for hours.
in the movie "Clerks'.... Dante's girlfriend says she hasn't been with many people but sucked 36 hotdogs and he's number 37... And then they fight and she leaves.. Then a customer starts following her outside.