Lady Gaga's every arch move seems designed to be parsed by graduate students convinced that mainstream America is scandalized every time someone plays with — all together now — gender. Meanwhile, in sold-out hockey barns across the land, thousands of tween Katy Perry fans — Katy Cats — sing happily along with "I kissed a girl/and I liked it," often accompanied by the moms and dads who've brought them to the show. If the 3D doc Katy Perry: Part of Me had stuck to the Hello Kitty! spectacle of her 2011 world tour, giving us a view you couldn't get in any arena, it might have been a blast. Instead the picture has the managed feel of a Vanity Fair profile, a familiar rise-to-fame and triumph-over-heartache saga. It doesn't plumb the self-regarding depths of Truth or Dare, and you can't imagine Perry becoming the bore Madonna has. She's happy to be a rock star, spreading her nonthreatening candy-colored inclusiveness. I didn't like the movie. I still like her. A pop star who can make you happy without making you feel like a sap is nothing to sneeze at.