I am not for hitting animals at all. That said, I have a kitten (the avatar!) who sometimes climbs my legs, especially when I have my PJs on the drawstrings around my waist are dangling. OUCH! Sometimes, people just react. I get him off of me and sort of just drop him down, and tell him NO. I am training him with a blow in the face along with the word loudly said - NO. He is now learning what NO means without the blow in the face. We also use a water bottle but he hates the blow in the face; the water, not so much! A friend of mine swatted one of my cats. I got so mad. I found out that he just didn't know better. That is what they did in his family. They don't hurt them, just give them a little swat. So, I guess it depends on how hard he did it, and judging from what you wrote, not that hard. What the kitten did was bound to have hurt your boyfriend more than he hurt the kitten. Talk to him about it and tell him that it bothers you to have the kitten get hit, and then work together to come up with something that the kitten really hates that you can both do to break him of this habit. Taz (my kitten) knows he will get a blow in the face - and I mean, gale force winds, not just some little puff - and then I say NO! and sometimes blow again. It is convenient b/c I don't have to carry anything around like a squirt water bottle. As long as he isn't abusing the kitten, and it doesn't sound like he is, then I would just tell him it upset you and that you want to find another alternative.