I just saw the clip and I'm afraid I don't see how this suggests she's got ticklish feet. She does place her bare foot on her other foot or leg (hard to tell), but it doesn't mean she's afraid of getting tickled. It's too brief to be able to tell whether she's doing it on purpose or if her foot just happened to move there. Besides, maybe she's just self-conscious about her foot being suddenly exposed like that. Maybe she doesn't like her feet. Maybe her foot was sweaty and she didn't want people to notice. Whatever the reason (if any), it's not really an indication of ticklishness. As for her expression, it can very well just be her reaction to the situation as a whole, and not a ticklish reaction. I also don't see hands all over her foot.
I'm not saying she's not ticklish on her feet. For all I know, she might have the most sensitive feet in show business (doubtful, but who knows). But I think interpreting this little scene as evidence/proof of her ticklishness is just wishful thinking.
That being said, while I feel stealing her shoe like that was a crappy thing to do, I must admit that this little scene is kinda neat. Although she looks a little pissed off when she shows her bare foot and throws her other shoe in the crowd (but I may be wrong). Otherwise, though, I don't like Katy at all. But that's just me.
