He had no idea what he was getting into when he allowed her to shackle him up.  He just finished telling her he could take anything a woman could dish out.  His mind was thinking sexually, of course.  Hers wasn’t.

Aww, you poor thing, does that hurt? Here, let’s make it even, I’ll let you kick me in the balls. What’s the matter? Oh yeah that’s right, I don’t have any! I guess that means I never have to hurt the way you’re hurting now. Isn’t that unfair? Oh well!