In the summer of 2007 I took my then-girlfriend into the college-themed area of downtown(clubs, bars, hippie stuff, etc). About an hour into our visit, we visit a record shop that's on a side street. My gf is a little parched from walking around in the summers heat, so I tell her that I'll get her something to drink from the coffee shop next door. As I'm exiting the record shop, there was a rather sickly looking black man sitting on the ground. He looks up, starts talking that he really needs some water, he's homeless, all this stuff. I agree and tell him to stay where he is. I grab a drink for the girlfriend, a big glass of water for the homeless guy, and some water for myself. I walked back up the hill to where the guy was waiting. He was already thanking me numerous times, I told him to not worry, as it was the least I could do. Right as I'm handing the water to the guy, a passing car had honked its horn at a car that was poorly parked, I had guessed. I had turned to look at the noise, obviously. When I turned back around, the water was gone, and he was gone. There were no alleys for him to run down, nothing. I turned all around, looking for him, but nothing! I went back inside the record shop, handed my gf her drink, and sipped on my water, basically ignoring what had just happened. So my gf picked out a few vinyl records and was ready to head out, no prob. We exit the store to head back to my car, and I wasn't about to tell her what had happened. As we were about to cross the street, the same homeless man walks by, water in hand, smiles at me and says: "thanks, hairbrush_repairman, you did good." I never told him my name.
I waited until we we were in the car before I told my gf about what had happened. I still don't really understand who that guy was and what his deal was.
TL;DR - I buy water for a homeless man and he basically disappears in front of me, only to reappear at a later time. He also knew my name.