”Friends”’ Rachel may have grown hers out, but the bob is still getting serious TV hair-play. Sela Ward recently revealed a smart, layered cut on ”Once and Again,” and ”Buffy the Vampire Slayer”’s Sarah Michelle Gellar hacked off her Rapunzel tresses in a post-Spike panic attack during the show’s Jan. 8 episode. Next on the chopping block? ”Sex and the City” hair-oine Sarah Jessica Parker, whose new tousled bob will be seen soon — but probably without any plotline to-do. Says an HBO rep: ”It’s really no big deal.” For Aidan’s sake, let’s hope Mr. Big agrees.