Every Saturday at midnight for the last six years The Hot Karl folks have started their gig by announcing that they're going to create the foulest, most disgusting fully improvised show in Chicago. Then they do it. The group's name comes from a sex act that involves pooping on your partner, and when I recently saw the show, the MC set the tone by asking for audience suggestions while riffing on the subject of fisting. The long-form improv that followed involved anal and oral sex, breast grabbing, and lots of dick jokes (hardly surprising since six of the eight performers were men). The material was very funny and very blue--much bluer than when I last caught The Hot Karl three years ago. The odd thing is that the grosser the players got, the more expertly they improvised: they were all in tune with one another, they never stumbled, and they treated the other performers' ideas with a respect only the best, most trusting troupes manage. Even an obvious accident, when one person initiated a montage sequence just when the scene was taking off in a different direction, was called back several times. Just as impressive are the rich, uncliched characters, deftly created almost as asides as the performers make their way to the next smirking reference to a muff or johnson. The sixth-anniversary show this Saturday, July 16, stars past and present ensemble members, including alum Frank Caeti, who's just been hired to join the cast of MADtv. Open run: Sat midnight. ComedySportz, 2851 N. Halsted, 773-549-8080. $10.