I don't know what to do about this.
There is this guy I know from high school that I regularly see around town. He is always with other people from high school, people he used to kick it with back then, who I also know, so when I see them I always say hi and chat with them for a bit. But this particular guy, every time I see him, brings up that he knows me since we were kids. He lived around the block and we "grew up together." He always mentions his sister and asks if I remember her, and I tell him that I vaguely do. When anything about childhood comes up in conversation, or even if it does not, he says something like, "Oh yea, I know that because we grew up together." This always throws me off because I don't remember this guy at all in my childhood. I remember meeting him in high school. I get lost in my thoughts, and I start doubting myself. Did I really know this guy in my childhood? I know the street he says he lives on, and he seems to know where I lived, but I honestly cannot remember having a friendship like that with this guy; I swear I met him in high school. It makes me uneasy because I start thinking maybe he is delusional and he imagined this whole story. I express my uncertainty and confusion to him, but have not challenged him or called out his bluff, out of caution just in case he is mentally unstable. It just really puts me in a weird situation. Or maybe he is just messing with me?