Heavy Rain/Funny

When Madison is questioning Paco for information at gunpoint, one of his guards knocks on the door to the room to check on them. So what can Madison do to make the guard go away? She starts making fake sex noises, and the guard walks off with a sly grin on his face. Paco's expression as she makes the noises right in front of him is priceless.
Ethan picking up one of his son's RC car controller, playing with the car, then putting it back where he picked it up from; on the floor.
The three cartoons you can watch in the game are hysterical.
The "psychology" option in the chapter, "Nathaniel".

Norman: Lt. Blake is gonna leave our planet and return to the Realm of Shadows. Creature of darkness, I beseech you to return to the Realm of Darkness, and leave our Nathaniel in peace.

- Even before that, when Blake breaks protocol and breaks into Nathaniel's apartment without any probable cause:

Norman: I'm not sure that's entirely legal.
Blake: ...call the cops.

Meta-example: play the Blues Brothers main theme during the first trial. You'll be laughing too hard to do the QTE.
The "aggressive" option in the chapter, "Kick Off Meeting", when Blake questions Norman if he's going to question everyone in 10 square mile zone.

Norman: It may not give us the address of the killer, but at least it's something to go on! Blake, if you've got a better plan, I'm willing to listen! Don't be shy, I'm all ears!

- Blake's reaction makes it even better.

Blake: FUCKIN' ASSHOLE!

Mad Jack is so stereotypical, it's hilarious
When Jayden first arrives at the police station you can sit down and play the virtual "bounce the ball off of the wall" game. If you do it long enough someone walks by and gives him a funny look, and we see Jayden seeming waving his arm around for no reason from her POV.