Spaceballs

This will seem strange, because it isn't one of the quotable lines you usually think of.

But, "That's gonna leave a mark" when Barf forgets the seatbelt. That bit is so classically John Candy. It may not seem like it, but watch the scene and see how he plays it. Subtle, which is so rare with a bit physical humor.

I laugh as hard at the way he delivers that otherwise not very funny line as I do almost anything else in the movie.

It doesn't hurt that the line itself has become a family in-joke of sorts. We've got kids in the family that use the line when they bump into something or whatever, that haven't seen the movie yet.

Now, the scene that makes me laugh the most is the "oh no, not again" bit in the diner. The whole scene is great, what with that reference to alien, the dancing baby xenomorph, and the Pullman/Candy reaction.

But the seatbelt line encapsulates what I've always loved about Candy.