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.
Even funnier if Grace is around to wonder if Ethan bought it for the boys, or for himself.
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 right now and return to the Realm of Shadows. Creature of Darkness, I do beseech you to return to the Realm of Shadows, 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!
The already rather Narm-y quote may become yet more humorous if you pick all the "calm" responses for Jayden, in which case he retains his cool, despite being frustrated…but Blake's line doesn't change, and it thus comes off as him flipping his shit for no reason.
Mad Jack is so stereotypical, it's hilarious
Look at the size of those lips!
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.
Even better... Watch the number floating near Norman's head - It goes up by one every time he bounces it off the wall. The counter itself is already over 20000. Just how long does Jayden normally get kept waiting?!
Ethan "evading" a SWAT team incompetent enough to make the Keystone Kops jealous. The crowning moment is him running just out of reach of a hapless, stumbling officer who shouts something that sounds less like an angry "Police! Stop!" than a desperate "Please stop!".
Jayden and Blake, if you choose the "ironic" response after not shooting Nathaniel:
Norman: Oh, I'm sorry! I thought you were a tough guy, a street-cop who's been through the mill. I didn't think you'd scare so easily.
Blake: Why don't you fuck off, Norman?
Norman's Troll-face is just hilarious.
A minor and easy to miss moment is if Ethan cooks Shaun a slice of pizza for dinner. Instead of eating it normally the kid will use a knife to cut it and eat it piece by piece with a fork in the same manner a person would eat a steak.
That is really just cultural dissonance; in most of Europe, it's quite normal to eat most food with a knife and fork like that, including pizza. Since Quantic Dream is a French developer, this is most likely just an oversight.