Jack's deadpan warning to Ethan about the explosive gum: "Just don't chew it."
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.
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!
Mission: Impossible: Ghost Protocol
In " 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: