The spirit of improv lives at the Sak Comedy Lab (380 West Amelia Street, 407-648-0001; www.sak.com), a 200-seat theater in, of all places, the base of a parking garage. Anyone who has seen the television show “Whose Line Is It Anyway?” knows the drill: a troupe of comedians spontaneously create skits based on audience suggestions. (Indeed, one of the show’s stars, Wayne Brady, is a Sak alumnus.) To get the crowd warmed up, Tootsie Rolls are tossed into the audience. And a box is placed over the heads of performers or audience members who say something too risqué, in scarlet-letter fashion. Friday night performances ($15) run from 8 to 9:30 and 10 to 11:30.