It's tough being a young celeb these days. You star in the hottest new movie (Kristen Stewart), or you're the biggest teen pop star (Miley Cyrus), or you're a new light on Broadway (Xanadu's Cheyenne Jackson), and then old people want to, y'know, ask you, like, questions and stuff. In the past week, we've seen how these performers have responded under such inhuman pressure. Jackson was caught mouthing the word ''bitch'' (playfully, we think) after Kathie Lee Gifford chided him for oversleeping and, presumably, arriving at the Today show late. Cyrus went on Ellen DeGeneres and had an interview-halting giggle fit when asked about her boyfriend. Twilight's Stewart slumped onto Dave Letterman's set and volunteered that she had no anecdotes to tell (''Did you tell somebody this?'' asked Dave, mentally firing a few of his producers). When Stewart said she was planning to drive to Russia from either London or Berlin, Letterman said, ''Let's hope for Berlin'' he and the guffawing crowd seemed to understand that there is automobile-prohibitive seawater separating England from Russia in a way Stewart did not. Finishing school and geography lessons for the lot of 'em, I say.