Funny / Halo 3

• The intro to the game is a monologue from Cortana (while we watch a shooting star descend from the night sky) explaining why she decided to work with the Chief rather than one of the many other Spartans. They're all very strong, very determined, very well trained. What does Master Chief have that they don't? He's lucky. Cue the falling star being revealed to be the Chief, in flames, falling form orbit and crashing to the Earth with all of the grace of a large brick.
• Johnson's classic difficulty changing dialogue returns, albeit a bit more subdued.
  Thel 'Vadam: "We must go. The Brutes have our scent."
  Sergeant Johnson: (Easy/Normal) "Then they must love the smell of green."
  Sergeant Johnson: (Heroic) "Then they must love the smell of hero."
  Sergeant Johnson: (Legendary, variant 1) "Then they must love the smell of bad ass."
  Sergeant Johnson: (Legendary, variant 2) "Then they must love the smell of bad ass. And I left a little present for you, Arbiter. And I'm walking away. Ha-ha-ha!"
  Sergeant Johnson: (Legendary, variant 3) "Then they must love the scent of testosterone."
  Sergeant Johnson: (Legendary, variant 4) "Then they must love the scent of a real man."
  Sergeant Johnson: (Legendary, variant 5) "Then they must love the smell of Bulgari. Yeah, I'm doing a little Product Placement! I gotta get paid, too!"
• The Easter Egg from versus play when you have flipped over an Elephant. "Hold RB to flip... wait, what?? How did you do that???"
• Something about the three-part Mood Whiplash between Cortana's monologue about how she chose John because he was luckier than the other Spartans... followed by John falling from the sky like a shooting star and plowing into the ground... followed immediately by Achievement Unlocked. An achievement for starting the game.
• When Truth broadcasts to the UNSC at beginning of Crow's Nest he goes on a long speech talking about how not even the "Demon" will survive the coming fire. The transmission cuts with both Johnson and Chief completely unimpressed.
  Johnson: Cocky bastard. Just loves to run his mouth.
  Master Chief: Does he usually mention me?
• The "password" Easter Egg starring various characters from Red vs. Blue:
  • Easy / Normal:
    Tucker: Hey, open up!
    Doc: Password, please.
    Tucker: You gotta be kidding me! What password?
    Doc: The password so we don't open the door for Brutes.
    Tucker: Do I sound like a Brute to you?!
    Doc: Well, you could be held prisoner by Brutes.
    Tucker: If I was held prisoner by Brutes and knew the password, then the Brutes could just force me to tell you the password and you'd open the door for them.
    Doc: ...Okay, well now I'm definitely not gonna open the door.
    Tucker: But we need ammo!
    Doc: Well why don't you go ask your Brute buddies, then?
  • Heroic:
    Simmons: Hey, open up!
    Grif: Password.
    Simmons: What?
    Grif: Need the password!
    Simmons: You gotta be kidding me! What password?
    Grif: Password! They gave it out at the staff meeting fifteen minutes ago!
    Simmons: Meeting? What meeting?! I was out here!
    Grif: Not supposed to let anyone in without it.
    Simmons: If the staff meeting just ended, no one outside is gonna know the freakin' password! Now open up! We need ammo and the Chief is out here!
    Grif: ...Does he know the password?
    Simmons: HE WASN'T AT THE MEETING EITHER!
  • Legendary:
    Church: Hey! Open up!
    Caboose: What's the password?
    Church: Password? Oh man, I forgot.
    Caboose: Forgot... what?
    Church: I forgot the password.
    Caboose: See, that was almost right. Uh, see, the password begins with "I forgot," but ends differently. Um, try again.
    Church: No. I mean, I forgot the password.
    Caboose: No, okay, see, you - you got it wrong again. See, you said the same thing as last time.
    Church: (sigh) I'm being serious; I don't know the password!
    Caboose:: No no, see, you changed the first part. See, that - that part was the right part. See, now you've got the whole thing wrong!
    Church: No! I forgot what the password is and I just need you to open the door!
    Caboose: ...Alright, c'mon, man, now you're just guessing!
• There is a saying: "Spartans never die, they're just missing in action." John-117 ends up actually MIA at the end.
• Then there's the "Annoying Grunt" Easter Egg.
  Grunt: Hey, Demon! The jerk store called, and they're all out of you! Poor you, stolen at the age of six and conscripted into the military, waaaaaah! (Beat) Okay look, you let me live, I got the Fist of Rukt. Look, I'll be at the bottom. I'll polish your boots. I'll polish your helmet! It's the gas, haha! When I'm on the gas, I don't know what I'm doing half the time!
• Quite a few of 343 Guilty Spark's lines are very hilarious, two good examples are "I told you to upgrade your combat skin!" when Master Chief dies near Spark and if the IWHBYD skull is active and you shoot Spark he may end up saying "That hurt my feelings. Oh my god, I have FEELINGS...!? I'm a real boy!"
• A somewhat meta example: the infamous IWHBYD^*  I Would Have Been Your Daddy skull, which was so well-hidden that nobody managed to acquire it until someone hacked the game code to discover its location. In order to get it, you have to jump through some of the holographic Halo rings near the end of "The Covenant" in a specific order. In other words, Bungie literally made you jump through hoops for it!
• This Brute line:
  -When this is over, that hammer… IS GOING IN SOMEONE'S ASS!!!
• The Chief proves he’s no stranger to sarcasm at the halfway point in "Cortana."
  Cortana: Got an escape plan?
  Chief: Thought I’d try shooting my way out. Mix things up a little.
  Cortana: *chuckle* Just keep your head down. There’s two of us in here now, remember.