Nip/Tuck's season finale which revealed that Famke Janssen's man-eating ''life coach'' Ava had once been, in fact, a man set the standard. Now it seems transsexuals are the new...lesbians? Cold Case's detectives recently unearthed a home-movie murder victim who looked like a girl but was really a boy, and the CSI gang solved the case of a transgender murder victim. Next up, ER's Jan. 6. episode will feature real-life transsexual actress Alexandra Billings as a patient with a unique diagnosis. How long before reality TV takes on trannies? ''Men fall in love with a beautiful supermodel...but she's a dude,'' mulls Veena Sud, who wrote the Cold Case episode. ''Oh, God, I hope not.'' Until sweeps week anyway.