Heard the one about the guy who walks into an agent’s office to pitch his family’s routine: a set comprising acts of almost unspeakable depravity? Come see ‘The Aristocrats’ and you’ll hear it a couple of dozen times over from some of America’s sharpest wits (Drew Carey, George Carlin, Robin Williams, the ‘South Park’ boys et al), in keys ranging from wincingly brutal to disarmingly affectionate. Like a basic jazz melody around which the performers improvise, the gag – an initiation rite-cum-secret handshake – prompts obscene litanies of alarming, even operatic proportions. There’s incest, bestiality, scatology and child abuse; a catalogue of choicest filth aimed first to shock and then amuse. For, despite its rep, the joke is infamously anti-climactic. At the most basic level, then, it seems that the comics here are really in it for the outrage (though whether the attraction lies in challenging taboos or demanding attention is another question). On the other hand, the fact that the material is devoid of humour makes its telling a real litmus test of whether a performer is truly funny. There’s also an intriguing suggestion that, as well as harking back to stand-up’s vaudeville roots, the joke appeals to the comedian’s inferiority complex – the idea of expecting applause for an activity they secretly suspect to be infantile, or beyond the pale.Constructed by Provenza and Jillette (Penn of Penn & Teller) from hundreds of DV interviews, ‘The Aristocrats’ offers formal variations on the theme (mime, playing cards), female perspectives on the subject and a killer Christopher Walken impression from Kevin Pollak. Its lo-fi, behind-closed-doors feel is apt to the tradition it describes, but after 90 minutes you’re more than ready to let some air into the room.