I'd often fantasized about having my face slapped. Either repeatedly as punishment or at random as a cruel surprise (being subjected to random, unanticipated cruelty is a huge part of my masochistic fantasy life).
The first time Alexandra slapped me I was more happy than hurt. Later I did confess (complain?) that the slap didn't really hurt much. Not long after she made her slaps more forceful. The next morning my cheeks still stung lightly something I greatly treasured.