I think that it's VERY inconsiderate!. Maybe you could embarrass him by serving very small portions because you have to now feed an extra mouth that you hadn't planned on. Why should you have to go out of your way to try to accommodate an unexpected guest? Put your foot down, and demand at least a one day notice. That doesn't make you a b*tch, but makes you look like a more gracious hostess, with everything well put together!

Fortunately, my ex never pulled anything like that on me. I trained him well!!