Thank you all for your input. For now I've decided to continue allowing it, and maybe ask for it. I don't know...

Someone mentioned that face-slapping was humiliating, but I don't find it to be. I thought it might be too violent, but it didn't really evoke feelings of shame. I'm only able to feel humiliated by my own actions, when performed under my own free will (ie, I would be ashamed of something someone forced me to do.) For those of you who think it is humiliating... why? Again, I'm curious.