Have you heard the one about the actor who auditioned only twice in 33 years?

It sounds like the start of a joke or maybe a sad tale, but for Bob Lohrmann, it's a happy truth. In 1975, he auditioned for People's Light and Theatre Company, a Philadelphia theater collective, and became a long-time part of its acting company; later he auditioned for the Philadelphia company of Paul Portner's "Shear Madness." After a few years of back and forth, he settled in to work full time for "Shear Madness" in Washington, D.C., first as actor (he's played all four male roles), later as associate artistic director, keeping it fresh.

He still does. That's why he's in Pittsburgh to direct yet another edition for the CLO Cabaret. The interactive comedy whodunit is in its 21st year in Washington (9,000-plus performances) and its 29th in Boston; it had another epic run in Chicago and has played in dozens more cities around the world, including at present Spain, Greece, Poland and Korea.

Lohrmann's directed some 16 or 17 productions in the U.S. and Canada, and in Washington he's trained the directors of a half-dozen foreign language versions staged in China (where they were uncomfortable with the audience voting that's part of the show), Iceland, Brazil, Turkey, etc.

His main continuing job, however, is to oversee the Washington production, which has two casts play some 13 shows a week.

Clearly "Shear Madness" is a phenomenon, one of those shows with proven audience clout that have come to Pittsburgh for long runs only since the Cultural Trust built the CLO a cabaret theater to house them.

"It's the only stable job I know of in theater," Lohrmann says over lunch. He had just been at the Cabaret Theater, admiring a barber's chair, circa 1910, just delivered for the set, featuring porcelain, real leather and a seat stuffed with horsehair. "What a beauty!" he exclaimed with the knowing enthusiasm of a man who's spent some 20 years connected to the comic portrayal of the hair business.

Has it gotten stale for him, after some 9,000 performances in Washington, in many of which he performed? Sometimes, he says. But he cites how much he laughs in rehearsal and says, "It's fun to watch the audience laugh." Then he imitates an older man he saw, "actually slapping his knees with laughter! -- what could be more fun than that?"

He says he has to remind the actors that, for all its comedy, this is "fundamentally a murder mystery." You have to feel the stakes. And then the audience chips in, helping to solve the crime

"Shear Madness" tailors its script to each city where it plays. The five local actors were each asked to bring 10 references unique to Pittsburgh, "and every day we're looking at the paper," Lohrmann says, to react to the news of the day. They even "bring in the weather" -- although "if it's snowing outside we've got serious issues," he jokes, because this run is due to end Sept. 28.

So while "they pay me good money to maintain the show, the actors have license -- even a mandate" to keep updating. He explains how every joke depends on its teller, delivery and audience, and that you have to try a joke three times to be sure it works. "If you've lost a laugh, the best place to look is the set-up. If that's not clear, you have no chance."

Among the script's new Pittsburgh details is the hair salon's location at 1818 East Carson St., a fictitious address. Suddenly, Lohrmann goes off on a tangent, describing how he loves the 19th-century buildings of Carson Street.

He says in casting here, he got all his first choices. They brought in "Shear" veteran Neil Casey to play the barber, but the rest of the cast is local: Tom Schaller, Ingrid Sonnichsen (who did the show for some 10 years in other cities), Greg Johnstone, Kristiann Menotiades and Mark Tinkey, with Jennifer Smith as understudy.

The seventh character is the audience, imagined as being present in a real working hair salon. After the murder is committed, a detective emerges, and what would in theater normally be an intermission is a break during which the detective interviews the audience "witnesses" to sample opinions.

The show is constructed so audience feedback effects the alternative paths it can take. Although there's an improv element, the cast has a good idea what clues, theories or evidence the audience will cite when asked.

A word to the wise: If you arrive 15 minutes early (the better to order food and drink), you'll see a pre-show, but if you don't, "you won't miss anything essential -- except a lot of fun."