Back to the Future: Biff and his kin repeatedly drive into trucks full of doon in various times. What's not to love?
Top Secret: A bunch of guys wizz on a statue of a penguin, then it drops a massive bird turd.
Problem Child 2: For some reason, the dog is paralyzed. When he's finally revived, after several days, he makes dookie that's about four times his size!
Austin Powers: The Spy Who Shagged Me: Lots of great poop humor here, from Austin drinking the liquefied doon, to Fat B*****d's many lines about having "a crap on deck that could choke a donkey."
Star Wars Episode I: The Phantom Menace Even a long time ago in a galaxy far, far away, unsuspecting guys can step in poop.
Billy Madison: "It's poop again!!" "He called the s***, poop!"
Jurassic Park: Even Laura Dern isn't hot when digging elbow-deep in a mountain of Triceratops patties.
Austin Powers: International Man of Mystery: Technically not a poop scene, but the whole sequence with the often underrated Tom Arnold encouraging Austin through what he thinks is a massive dump is classic. "Who... does... Number Two... work for?"
Dogma: An entire demon made of plops. Need I say more?
Star Wars Episode II: Attack of the Clones: The whole movie, but especially that great poop scene when C-3PO is in the droid factory.