sennen goroshi
A japanese practical joke where one sticks their fingers up one's behind. Is made even more popular from it's appearance in the popular anime known as 'Naruto', where Kakashi uses the technique on Naruto, addressing it as his "One Thousand Years of Death" technique.
Boy: Urgh, my ass hurts like hell. Jerry just had to perform the 'Sennen Goroshi' on me.