How do I politely reject a guy firmly.

I'm 16, which did not deter him he brought up that it's technically age of consent in my state but I'm really not interested.

Basically, there's this guy at the supermarket I work at who will not stop asking me out, following me around in the store. He stopped me when I was leaving, saying where you are heading, are you meeting up with good friends or bad friends. Offering me rides home.

Last week he bought me flowers and chocolates. It's getting to a point, but I don't want to get murdered in the parking lot so how's a way i can do this.