I agree with Wind_Drift. He entered your encounter, so he should mind his manners lol. What you do about it is totally up to you, and anyone knows that could range from nothing up to killing the guy. I suppose tag-following him is included.
I will expand on this though if you don't mind, since it's related. I was mining on Junktown quarry. I was bluesuit with only a hammer, going back-n-forth between two rock clusters that were close together. I parked my mining cow in between them. So I would hammer here, hammer there, stop at cow and repeat. Along comes some girl who runs up between the rocks, right along side my cow and she starts hammering one of my two rock clusters. "Well", I say to myself, "it's a public place so she can mine here too", and I don't have exclusive claim to these rocks so whatever. I say hi and she says hi. Then she realizes that I am not going to stop my process just because she's there, and we find ourselves hammering the same rock pile. She then calls me rude. LOL! I stop to explain and we became friends, fell in love, got married and now have 3 kids.