In Absolution, at the end of the orphanage mission there's a cutscene where 47 points whatever weapon he's holding against Lenny. The funny thing? He can point him with his fiber wire, a robot toy or even a book! And if you keep the priest suit while holding a book? You get this result.
In Blood Money, you can complete one particularly grim mission (killing an FBI-protected witness in his home, in broad daylight, during his son's birthday party) while dressed as a clown.
The same level allows the player to obtain a child's air rifle, for use in any level.
Joseph Clarence can see it in your eyes - you're not a bald man - bad man...
The mission "Flatline" in Blood Money. 47 begins to yell then stops, having resigned himself to the fact that he's just going to have to rescue Agent Smith for the umpteenth time. Made more jarring when Smith speaks, sporting a far more cynical and self-aware tone of voice than in other instances.
The Chef's rant in the beginning of Absolution. As if hearing him boast about his cooking skills isn't hilarious enough, putting him to sleep shortly afterwards could make you lose your concentration from laughing so hard.
If your sense of humor is particularly dark, there's Prostate Cancer Guy (see the Memetic Mutation entry in the YMMV section).
Also, the court scene with the obvious Schizophrenic guy and the Prosecutor trying to get the judge to commit the man already. If you disguise 47 as the judge you get to pass judgement on him, 47 dismisses the case causing the man to start dancing around the court while the prosecutor exclaims "What the hell was that shit!?"
While in the corn field with the Saints trying to kill you one of them goes on a rant about how 47 is completely surrounded and is doomed. And that's when you can garroted her while she's saying this.
You can also kill the leader of the Saints by sniping a crane holding corn when she walks under it. The funny part is that she screams likes a little girl as it falls on her.
In the "Hidden Valley", "At The Gates" and "Shogun Showdown" levels of Silent Assassin, the blow of being so frequently spotted gets softened by the rather unintentionally hilarious alert message when disguised as a guard:
"Travis to Praetorians: we are on high alert. Dig in and shoot anyone who approaches. We are the best, and now is the time to prove it!" If you time it right and shoot well enough, all the elite, unstoppable "best" will be dead by the time Travis has spoken the last two words. Doubles as a CMOA, natch, but it's kind funny hearing him boast and bluster into a dead radio...
After 47 gets captured in the basement of the police station, Dexter and Skurky interrogate him on the whereabouts of Lenny. After 47 headbutts him in response, Dexter starts hitting 47 with the first object within reach; it's not until a few slaps later that he disgustingly realizes that it's actually one of Skurky's sex-toys.
Most of the target's dialogue falls under this heading, too, especially around the point that Lenny gets desperate enough to offer you a reacharound.
Every single point in which Lenny gets a Hope Spot: first, he finds some cover behind the stagecoach and opens fire with a derringer, all the while gloating that you're nowhere near as brave as him; not only do all his shots miss, but you can easily just walk up and take the gun off him, changing his tune magnificently. Secondly, if you chase him around long enough, he'll actually manage to limp over to 47's car... only to find that the door is locked and the keys are not in the ignition, much to Lenny's hysterical frustration. Thirdly, he finds a tomahawk embedded in a tree just a few yards away, but it's embedded too deeply for him to retrieve it even after several minutes of straining; hilariously, you can retrieve the tomahawk yourself very easily- and hack him to death with it. Fourthly, you can shoot the vultures instead of him, resulting in the aforementioned killer ice-cream van. And finally, you can just get in the car and drive away; cue panic attack as Lenny realizes that he's just been trapped in the middle of the desert, without food, water, a shirt, or a signal to his phone. For extra fun, remember that he'd been begging 47 to drive away prior to this point.
Made even better when you notice that 47 appears to actually take a step away from the dude!
One of the many, many ways of assassinating Layla Stockton is the "Savage Sushi" challenge, where 47 steals U'wa Tribe Poison from Dexter's armoury and apply some to her sushi. However, instead of causing immediate death like most poisons in the Hitman series, this particular toxin causes hallucinations first, leading the target to wander out onto the balcony, disoriented and giggling at visions of ladybugs gathering above her head. The whole thing ends with Layla, having decided that she has wings of her own, taking a flying leap to her death.
Best of all? Instinct mode allows you to see the ladybugs.
Diguising yourself as a Scarecrow allows you to prove just how good 47 is at impersonating inanimate objects; not only are the guards fooled, but so are the crows- which actually use you as a perch as time goes on.
In the level "A Murder of Crows" in Blood Money, if you walk into one of the clubs and wait around for a while, 47 will eventually start dancing, all the while keeping that straight, emotionless expression on his face.
Similarly, in the "Shangri-La" portion of the "Run For Your Life" mission in Absolution, you can find a dance floor with music equipment in one of the rooms. If you walk up to the synthesizer, a button denoting "HIDE" will show up. Press the button, and watch as 47 starts getting down with his bad self. Again, keeping a straight face.
47 also finds himself dancing in Blood Money in the level "Till Death Do Us Part". If 47 goes onto the dance floor and waits for a while, a woman that didn't have any partner steps up and starts dancing with with him. And he has a completely deadpan expression the entire time.
During the Blood Money level "Til Death Do Us Part", the groom will occasionally sit down and "play" the piano. As seen in this Silent Assassin run, with a well-placed mine, you can drop the chandelier on him. "YEE-" *SPLAT*
One route to the chandelier hoist in the Blood Money level "Curtains Down" passes directly through the opera house's women's locker room. Just try not running through it.
A number of conversations in Absolution are hilarious.
Oh god yes, the conversations are some of the funniest parts of the game. Take this one for example:
Cop 1 (All of them are watching a porno): The things that people do to get on camera these days.
Cop 2: Yeah. Hey, you know what we should do? Stop watching. Just stop.
Cop 3: Hey, you're right! we could start a, what's it called, a domino effect. We owe it to the youth of America.
Hotel Clerk (In the single most Camp Gay voice humanly possible): Have you seen those steel monkeys carrying around enough guns to start world war three? And you're asking me if I'd rather be outside in the rain? Uh, hell yes!
Cop: Woah, okay okay, chill out.
Hotel Clerk: Don't you tell me to calm down! I know my rights, and i'm sitting here with people bitching at me about not being able to get into their homes!
Scientist 1: Did you hear? Steve got clearance to the Omega Facility.
Scientist 2: Really? Is that what they're calling it? Sounds like a trashy airport novel.
Scientist 2: Wait, I can see it now. (Does his best announcer impression) When a CIA agent is found dead on a pier, renegade journalist Jack Benson returns to face his personal demons and uncovers a secret file that reveals that shadowy government organization only known as...The Omega Facility!
Patron: "Yeah. So when in the hootenanny are you getting more ammo?"
Clerk: "In a week or two, and that's true!"
Something else that makes the conversation hysterical in hindsight: you get the meet the crazy gnome guy in the courthouse level...but before that point, it's pretty easy to assume they're talking about Dexter!
One way to deal with Bill in the Chinese New Year part of "Hunter and Hunted" is to steal Birdie's file. The reason? A crooked cop is trying to sell it to Bill, and when they go to look at it and it's gone, Bill assumes it's a setup - and pulls his gun on a police officer. Needless to say, he doesn't survive. Always fun when someone else does your dirty work, isn't it?
In Blood Money, the final mission has a fairly useless glitch which requires very specific circumstances to work, but is worth trying solely for the spectacle alone. You must wake up from your faked death, kill all the guards present but not Alexander, and lure him over towards the stairs on the far side of the room, leading down. He'll slowly give chase in his motorized wheelchair. The stairs have no wheelchair ramp. Enjoy a cheat-assisted display of the glitch here.
When Etrigan the demon fights the alien parasite who gave Tommy his powers at a gangster's funeral (the same gangster that Tommy was hired to kill). Yes, it's exactly as Crazy Awesome as it sounds, and is very funny.
Green Lantern: Your murder express just ran out of highway, Monaghan! This is one guy you won't be adding to your bodycount! Time to scratch Green Lantern off your list!
Tommy: Don't you mean railroad?
Tommy: Well, if it's a murder express, ain't it gonna be on the railroad an' not the highway? Don't see too many trains on the interstate, right? Unless it's an express bus, I guess. Is it a bus?
Green Lantern: What are you talking about?
Tommy: Just curious.
When Sixpack goes to get The Defenestrator, one of his old teammates, out of Arkham Asylum. (Keep in mind that Sixpack is a fat, drunken homeless man in a soiled, ridiculous superhero costume.)
Sixpack: He's needed, Doc. Badly. How soon can ya let him go?
Doctor: I dunno about that. We got pretty strict security procedures here at Arkham... On the other hand, you seem like a pretty responsible guy. What the hell, huh? Sign here, here, here, and here and we'll release him into your care.
The rhyming narration of the Christmas issue In The Style Of "Twas the Night Before Christmas."
"Word!" said his homie, "I got my nine! Now let's go bust a cap in that nuclear swine!"
Tommy killing a vampire by blowing his arms and legs off with a shotgun and leaving the limbless torso in the street to wait for sunrise.
The JLA crossover where, after Batman has angrily informed the rest of the Justice League that Tommy is a hardened, ruthless assassin, Superman — who is unaware of Tommy's profession, has missed this entire revelation and once had a friendly conversation with him on a Gotham rooftop — enters the room and greets Tommy like an old friend. As Tommy and Superman catch up, the rest of the Justice League just gape in astonishment.
Tiegel's confession of virginity to Tommy. After a few minutes pacing on the carpet, trying to work out how to phrase it, Tommy surprises her and...
Tiegel: "Ah! Monaghan! I've never made sex before!" Tommy: "... Made sex?"
In a brief moment of levity before the final bloodbath, Tommy attempts to save Hacken's life with a Tap on the Head.
Hacken: "Holy Jeez, Tommy, someone just hit me over the head! Did you see who it was?"