Turn up late and you'll miss the superior opening act on this double bill: Cook County Social Club, whose four performers, directed by Jeff Griggs, are as brazenly committed to improv's "affirm everything" mantra as any I've seen. Their dark, flamboyant comic sensibilities clearly aligned, they orchestrate black-comedy vignettes tethered to richly odd characters, such as ham-fisted apprentice barbers. But what most impressed me was how fluidly and creatively they transitioned between scenes, usually dangerous improv moments. In the less engrossing but entertaining Concept Album 2: Shuffle, the BBC Comedy Troupe improvises to songs randomly played from an iPod. Though it can be unwieldy to deal with nine members, at times they channel their energy to great effect. Through 3/10: Fri midnight, I.O., 3541 N. Clark, 773-880-0199 $5.