Bad Touch!

How do I tell people not to touch my belly?! I've finally poked out enough at 25 weeks that people notice my baby bump before anything else, but their first instinct is to reach out and touch/pat/rub it. 
My husband says "it's just comes with the territory," but it feels invasive to me. My stomach has always been my least favorite part of my body, and even though I've been wanting my bump to show, I'm not comfortable with people just touching my stomach so intimately. 
(Also, the first person who has grease or anything dirty on their hands and touches my clothing...mama does not handle her anger well right now. Just saying)
So. Do I just plan to offend everyone? Or is there a kind way to say all of the above?