The Aristocrats (2005)

A whole film about one joke. Dozens of comedians tell the same filthy, ancient backstage gag, each in their own way, and the real subject becomes performance itself: how timing, voice and nerve turn identical words into wildly different results. It is a masterclass disguised as a dare. Be warned that the material is as crude as it gets and repeats by design; if that sounds tiresome, the craft discussion between tellings is what keeps it fascinating.