You see someone whom you briefly talked to online/over the phone in the grocery store (or some other public place). He walks up to you and says, "Don't I know you from somewhere?" One could certainly say, "Sure - we met on Plenty of Fish a couple of years ago. We talked on the phone once and you never called again. I took an inkblot test shortly thereafter and they said I was normal, so I don't know what your problem is."
On second thought, that's probably not the best course of action.
I made a few broad statements to clue him in on who I was. No dice. He gave me his card, and asked that I sent him a friend request on Facebook. Now it's my turn to be the flake. #karma #yeahbaby #imnotcallinghim
How would you react if this happened to you?