Is it normal a flat earther invaded my "personal zone" ???

So I have two jobs and one of them is a part time sales associate. I work the checkout at a food shop and this guy comes up to my register all normal at first. On the counter, we have pens with tiny rotating earth globes attached to the tops. The guy puts down his items to buy and then laughs as he takes one in his hand. I smile and ask him what's so funny. He then tells me how it's funny they "still sell earth related items that are round". I then asked what he meant and he told me "the earth isn't round, it's flat". I laughed and he then said something like, "I'm serious, the earth isn't round, it's flat".

So I stop smiling and ignore him because I assume he's crazy. He then tells me how he's a member of the flat earth society and that there are about a thousand or so people who are not ignorant who understand how the earth really is. So I got annoyed with him and said "nice joke". He then got in my face and waved his hands around and took out a card that had "flat earth facts" on it. He told me to go to his blog and read about the theories that exist. I told him that's crazy and I refuse to look up that nonsense. He then walks over around the checkout counter and up to me and puts his hands on my shoulders. At this point, I FREAK out and yell for my coworker nearby. He then tells me I'm a sheep and he's the wolf and leaves.

I went on his blog and looked up this society. Apparently they do actually believe the earth is flat and that NASA is lying to us. What good would it do for NASA to lie about the shape of the earth? I don't get it, IIN?