The infamous invention of the ingenius Weasley twins, from the popular fantasy series Harry Potter. As its name implies, U-No-Poo causes the unfortunate victim to have certain...difficulties with his or her metabolism. I am sure that a more explicit explanation is not necessary for the time being.
"Why are you worrying about You-Know-Who? You should be worrying about U-NO-POO -- the constipation sensation that's gripping the nation!"