Mel Gibson was supposed to play the tattoo artist, but the idea was later dropped following protests from the cast and crew. He was replaced by Liam Neeson. Director Todd Phillips later wanted to reshoot Neeson's scene, but Neeson was unavailable to return, as he was filming Wrath of the Titans (2012). The scene was subsequently reshot with Nick Cassavetes in the role.
The three Billy Joel references in the movie (a "Glass Houses" poster in Alan's room; the song "The Downeaster 'Alexa'" on the soundtrack, and the parody of "Allentown" sung by Ed Helms) stemmed from Todd Phillips's desire to decorate Alan's bedroom with the poster, feeling that Alan would strongly identify with it.
As the Wolf Pack enter the Buddhist monastery Zach Galafinakis is seen performing a Christian cross, he actually performed a Greek Orthodox sign of the cross consistent with his Greek origin and faith.