Pussy
First of all, it has no relevant resemblance between a female body part and the act of hesitation. Second, why do we even call people, "pussies," "wusses," "wimps." If someone doesn't want to do something, why ridicule them? You could simply encourage them, or just leave them alone. It's a form of bullying.

I know I'm no exception. I tease people all the time, but there's no sense in going over the top and just discouraging someone. It sounds pretty cheesy, but all facts present, there's no purpose in discouraging anyone.