mc5 - I'm not wearing any pants!

Take a familiar (or at least famous) quote (e.g. "Don't go around saying the world owes you a living. The world owes you nothing. It was here first." by Mark Twain). Then find a good stopping point (e.g. "Don't go around saying"). After this, add the phrase, "I'm not wearing any pants (e.g. ""Don't go around saying, "I'm not wearing any pants!").

Stevie

Double, double, toil and trouble
Fire burn and cauldron bubble
Eyes of newts and legs of ants
Macbeth's not wearing any pants

W Churchill

We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills, even when we're not wearing any pants.

blamelewis

I have in my hand a pair of pants... (Striving for accuracy in the pursuit of the trivial I find from my meagre researches that Chamberlain's famous quote seemingly isn't in fact a quote. However as Humph used it on Clue I reckon it's ok...)

Geo

...and now class: to demonstrate Newton's Third Law, I am not wearing any pants.

Stevie

I know what you're thinking, punk. You're thinking "did he fire six shots or only five?" Now to tell you the truth I forgot myself in all this excitement. But being this is a .44 Magnum, the most powerful handgun in the world and will blow your head clean off, you've gotta ask yourself a question: "Why ain't that cop wearing any pants?"