To be the devil's advocate here, but how would he actually know that the cells came from your skin? Unless he took the skin cells from you himself, he wouldn't. Having some person send you "skin cells" in the mail isn't empirical evidence. Unless he could, without a doubt, identify where the cells came from, just looking at cells under a microscope proves nothing.

DH: I know this. I am trying to draw him out. Note that I have shown him an article about multinuclear cells. I have no idea what his game is, but I've tried to be polite.