Last night, my friends and I were on the way home from hanging out. My guy friend, whom I kind of like, was driving, my sister was in the front passenger seat, and my other guy friend and I were in the back. Partway home, the guy I was in the back with leaned over and put his head on my lap. He then started running his fingertips over my legs, mostly on the tops of my thighs, but also my inner thighs, knees, and calves occasionally. He didn't go any higher than mid-thigh, but it still kind of creeped me out. However, I also felt like there was no good way to ask him to stop. He asked me if it was bothering me, but for some reason I said no. It also creeped me out that he stopped doing it when my sister turned around to see why he'd gone quiet, then started again when she looked away. I'm 17 and he's 21, and he is a nice guy who seems to care about me, so I don't think he has any more-than-platonic feelings toward me, but he's done things like this before too, and I don't understand why. Is what he did a normal thing that opposite-sex friends do to each other? If not, then in case he does it again, how should I ask him to stop?