When I mention this to my husband

Maybe I'm assuming that "mention" means you say it "in passing" or in a deferring manner, but don't "mention" it - fucking demand what you want. Tell him that you HATE when he talks to other people about YOUR body - YOUR ass - and that you are telling him, not asking him, but telling him to stop immediately as you consider it private and you consider it demeaning to have him say that and then feel all those people's eyes roaming over your ass after he says such things.

he somehow ends up hurt and thinking I don't like his physical affection

Sit him down and tell him it's time to have a rational conversation. Start off by telling him that you love his physical affection but some things are going to have to change - and there is no point in getting feelings of hurt or rejection over the matter as that is completely not what the issue is about. The issue is about appropriate behavior in public and in front of kids. Tell him you want him to love your ass for the rest of eternity and that he can have as much of your ass as he wants as long as it is in a private context. When there are other eyes in the room - ANY other eyes, be it kids or friends or strangers - that your ass is OFF LIMITS both in terms of physical contact and in terms of any mention in conversation. Tell him that your ass is for him only and absolutely no one else. If his feelings are hurt then he needs to think about it for a couple of days - think BEYOND his feelings and start thinking of YOURS.

Set the boundary and then enforce it. Set the boundary. Enforce the boundary. This is YOUR body. If he gets his feelings hurt over this tell him that sometimes people have to examine their feelings rather than just give in to them. You're not trying to reject him - you're establishing a boundary related to YOUR body and what you are comfortable with other people seeing and hearing about YOUR body. It's not about his affections - it's about your body.