I hate it too. I made my feelings very well known early on though via a funny story.

A lady at my work who I barely knew one day came up to me and started rubbing my belly, quite seductively I thought, while I was on the phone. I was furious so i put the call on hold, and before she could say anything I said "My boobs have gotten bigger too, would you like to grope them too?"

Needless to say she never spoke to me again

I then retold the story quite proudly ta MIL's house and my BIL and SIL took the hint and stopped trying to grope me every time I saw them.

Second pregnancy I also made myself a t-shirt with an iron on transfer that said "NO you can not touch my belly!"

hope that helps!
xxxCaz