Ticklish in an odd place

This may be a weird one but it's bothering me and my boyfriend most likely. So I love it when my bf fingers me, but lately I've noticed that when he 'hooks' I guess on either side (not front or back, it tickles like hell! It's actually hard to avoid and I feel bad for having to grab his hand and pull it away. It's just really uncomfortable for some reason idk why! Has anyone else experienced this? Is there some way to avoid it or become "desensitized" to it I suppose?