DIRTY LITTLE SHOWTUNES, at the Theatre Building. Aggressively gay, this charmingly bold parody revue features witty, often explicit lyrics by Tom Orr set to classic Broadway and operetta tunes. In the spirit of Gerard Alessandrini’s Forbidden Broadway, “Show Me” from My Fair Lady morphs into “Show Queens!” and “Mame” becomes the tell-all “Nude!” We also get the stereotype-ridden patter song “I Am the Very Model of a Modern Homosexual,” “How Do You Solve a Problem–Gonorrhea?” and “Everyone Was Beautiful at the Bathhouse.” Orr takes well-aimed potshots at Andrew Lloyd Webber (for endlessly repeating tunes that were never very original), at the overdone marketing of gay pride memorabilia in “Almost Over the Rainbow,” and at the feud between the leather and drag subcultures in “The Leatherman and Drag Queen Should Be Friends.” Less mainstream are his tributes to fellatio (“Gotta Have a Gimmick”) and 900 numbers (based on “The Telephone Hour” from Bye Bye Birdie) and his deconstruction of the cults of Barbra Streisand and Judy Garland.