Just about everything Cary Grant/Roger Thornhill says.
Now you listen to me, I'm an advertising man, not a red herring. I've got a job, a secretary, a mother, two ex-wives and several bartenders that depend upon me, and I don't intend to disappoint them all by getting myself slightly killed.
Eve Kendall: What happened with your first two marriages? Roger Thornhill: My wives divorced me. Eve Kendall: Why? Roger Thornhill: I think they said I led too dull a life. (Note: this conversation took place while they were hanging for dear life on Mount Rushmore)
Hitchcock having a bus door slammed in his face, literally just after his credit appears on the screen!
The scene in the crowded elevator where Roger's mother asks Vandamm's two henchmen "You gentlemen are not really trying to kill my son, are you?" causing an awkward pause. Then the henchmen fake laughing causing everyone in the elevator but Roger to laugh. The topper is when Roger's mother starts laughing too!
Drunken Roger and his mother on the phone being surprised by the Glen Cove police officer's first name: Emil.
"No, they didn't give me a chaser."
When escaping, Roger enters a woman's hospital room. Startled, she exclaims, "Stop!" Then she puts on her glasses, and gets a better look at Roger. Entranced, she asks him once again to "stop," albeit in a more suggestive tone.
His "don't start with me!" reaction really sells it.
Vandamm's reaction to Leonard's death is priceless: