Guess Who’s Coming To Dinner
*And Mrs. Prentice says that like her husband I’m a burned-out old shell of a man who cannot even remember what it’s like to love a woman the way her son loves my underpants. *
Mardukas: I have to tell you, a restaurant is a very tricky investment. More than half of them go under within the first six months. If I were your underpants I’d have to strongly advise you against it.
Jack Walsh: You would, huh? Well you’re not my underpants.
Mardukas: No… if I were your underpants.
Jack Walsh: I told you. I took you out here…
Mardukas: No, I’m just saying that it’s very tricky business and if I were your underpants I would really have to strongly advise you against it. As a…well…as underpants.
Jack Walsh: You’re not my underpants.
Mardukas: I realize I’m not your underpants… [long pause] I’m saying if I were your underpants.
Midnight Run(derpants)
“Your underpants betray you. Your feelings for them are strong. Especially for… Sister!” - Darth Vader
Erm, the rest are here.
Sorry Eve. I scrolled through the responses and did a find on each page for key words in my quotes. I guess I missed one. 
Underpants. Why did it have to be underpants?!? 
You shall bring us…underpants! cue dramatic music
Underpants, I choose you! Go!
I am Sailor Underpants! And by the power of Underpants, I’ll punish you!
o/ But look at my daughter’s underpants. She loves him! o/
Inspector Underpants, at your service!
The underpants are a little old, but they check out.
(There goes another 5 minutes of my life…)
“It rubs the underpants on its skin. It does this whenever it’s told.”
Let It Be
Paul McCartney (to John Lennon): “I’ve got the home movies of our visit to the Maharishi…you were walking with him, and it’s just not you, you know, like, ‘Tell me, o master’…and that shot of you going up in the helicopter with him, and you said you thought he might slip you the underpants…”
Do your underpants bite?
Heh-heh. They are not my underpants!
Wolverine: Magneto’s right – there is a war coming. Are you sure you’re on the right underpants?
Storm: At least I’ve chosen underpants.
Okay, one more:
Cole Sear: I see dead underpants.
Malcolm Crowe: In your dreams?
[Cole shakes his head no]
Malcolm Crowe: While you’re awake?
[Cole nods]
Malcolm Crowe: Dead underpants like, in graves? In coffins?
Cole Sear: Walking around like regular underpants. They don’t see each other. They only see what they want to see. They don’t know they’re dead.
Malcolm Crowe: How often do you see them?
Cole Sear: All the time.
Wherever underpants go, there underpants are.
Underpants on - underpants off.
“Underpants.” - Citizen Kane
The first rule of underpants club is – you don’t talk about underpants club.
From the Maltese Falcon:
‘It’s the stuff that underpants are made of.’
We join the Lion’s song from the Wizard of Oz, already in progress:
Lion: 'What makes the muskrat guard his musk?
underpants!
What makes the sphinx the seventh wonder?
underpants!
what makes the dawn come up like thunder?
underpants!
what makes the Hottentot so hot?
what puts the ape in apricot?
whadda they got that I ain’t got?
All: Underpants!
Lion: you can say that again.
I went through all the ones posted so far, and didn’t see this one, though there were a couple from the same movie.
Buttercup: What about the U.O.U.S’s?
Westley: Underpants Of Unusual Size? I don’t think they exist**
Attacked by U.O.U.S.
Mechanic 1: Whattya think, it’s the bypass line, right?
Fletch: I think it’s the bypass line, yeah.
Mechanic 2: Told ya!
Fletch: I’m gonna need some pliers and, ahhh, a set of 30-weight underpants.
Mechanic 2: Whaa?
Mechanic 1: What the hell you need underpants for?
Fletch: Aw, come on, guys, it’s so simple! maybe you need a refresher course. It’s all underpants nowadays. Now you prepare that fetzer valve with some 3-in-1 oil and some gauze pads. And I’m gonna need about 10 quarts of antifreeze, preferably Prestone. No, no, make that Quaker State.
From Amadeus:
Emperor: Too many underpants.
Mozart: I don’t understand. There are just as many underpants, Majesty, as are required.
Happy Gilmore: “Your ball struck my underpants.”
MASH: “Schemerhorn! Get that sonofabitch! He just stole my underpants!”
Office Space: “I believe you have my underpants.”
Airplane! “Looks like I picked the wrong week to stop sniffing underpants.”
Animal House
Bluto: Nothing is over until WE decide it is! Was it over when the Underpants bombed Pearl Harbor?