Jack's deadpan warning to Ethan about the explosive gum: "Just don't chew it."
In the climax Ethan is nearly killed when he hooks the line from the helicopter Jim Phelps planned to escape in to the back of a speeding train as it enters the Chunnel and blows it up. When it's over the camera pans from Ethan on the outside of the rear car breathing a sigh of relief to a shocked train conductor inside who had witnessed the whole thing and promptly faints.
As the disavowed team is about to go into full silence mode for the Langley heist, Krieger sneezes loudly, causing their sound meters to briefly go haywire.
Ethan: Krieger, from here on in...absolute silence.
(Krieger nods, then gives his giant nose one last wipe)
The poor CIA employee getting hit with the sickness fluid. At one point during the heist, he emerges from the bathroom thinking it's over, takes two steps, and promptly runs back into the bathroom.
Mission: Impossible II
In the second film, Ambrose and his crew catch up to Ethan trying to get Chimera out of the building it's housed in, causing a huge firefight; Luther is unable to warn Ethan beforehand because he was tied up getting out of the van as a henchman had put a bomb on it. As Luther finally escapes the rubble, Ethan has already been pinned behind cover from being outnumbered. Ethan then gets a warning from Luther that Ambrose was on his way up.
Ambrose's remark that the hardest part about impersonating Ethan was "Grinning like an idiot every fifteen minutes". The sheer venom in Dougray Scott's voice is what sells it.
Pretty much all of Anthony Hopkins limited screentime but special mention goes to, "To go to bed with a man and lie to him? She's a woman. She has all the training she needs." He gets the film's best line with "This isn't Mission: Difficult. It's Mission: Impossible. Difficult should be a walk in the park for you."
Mission: Impossible 3
As Ethan escapes IMF HQ in the third film, he jams the walkie-talkies by holding down the talk button, disabling Brassel's ability to communicate with security. As Ethan comes out of the cover building, he pins the walkie-talkie next to a radio playing "We Are Family" on his way to freedom. Brassel is in disbelief as the song comes over the walkie-talkies, turning to his partner stating, "You have GOT to be kidding me."
"Turn the switch on and off. Don't forget the off." Such a serious line delivered so seriously shouldn't be funny, but it is!
"I'm going to die unless you kill me."
While instructing Julia how to use a gun, she doesn't realize she's pointing the gun at him.
When Ethan!Davian gets in the Lamborghini with Zhen and Luther opens the pothole below the false console of the car.
Ethan!Davian: What's up?
Luther: Nothing, what's up with you?
Ethan!Davian: Nothing. *climbs down into the hole*
Mission: Impossible: Ghost Protocol
At the the world's tallest building in Dubai, Benji returns to the room and sighs with relief: Changing all those room numbers was really hard! Meanwhile, the rest of the team is collapsed on the floor after Ethan almost plunged to his death, and Brandt and Jane almost died saving him. They are decidedly unsympathetic.
The reason he has to pull this death-defying stunt is because the rope he was using to climb down wasn't long enough. When he realizes this, he's about ten feet above the open window he needs to get through, and this conversation occurs: