How to get a guy to stop calling me nicknames?

This guy and I have been talking for awhile and he's super sweet, funny and charming. We're still in the flirting and "getting to know each other" stage so it's not serious. The only thing that irks me is that he calls me "baby" and "sweetie". Idk why but, those two nicknames make me cringe. How do I tell him I'm uncomfortable with these w/o sounding rude and unreasonable?