Don't you hate it when you meet someone at a one day class/workshop, but then promptly forget about them the second you leave, because you have the memory of a goldfish and don't actually like meeting new people? Well, this part isn't so unpleasant. Something you don't know about isn't going to harm your mental comfort.
But then you're at the grocery store or something, and they walk up to you and go, "Hey *insert your name here*!"
Your initial reaction is something similar to deer in headlights, because some random stranger has started talking to you, and you're envisioning a man in a trench coat offering you candy next to a van with painted over windows.
"How's it going? Man, it's been a while."
Then you calm down a bit, because you realize you must know them from somewhere, and you take a few unsteady breaths to dispel the adrenaline that was about to make you either run faster than superman or suddenly become paralyzed.
At this point they start talking about something funny or cool or really stupid for about a minute, but you stop listening because after the calming realization that you know them, you panic again, because you can't remember their name or where you know them from.
You rack your brain for their name at least, but when nothing is forth coming you just start listing names in your head that may go with their face.
This is usually when you realize that there's been an awkward pause in the other person's rapid speech, and you don't know what you're supposed to respond with. So you laugh, hoping it was a joke, but the other person just looks slightly offended at this and you hope against hope that she didn't just tell you about how her pet cat died.
In a desperate attempt to free yourself from this awkward situation, you pretend to check the watch you're not wearing, mumble something about being late for your shopping errand, return your shopping cart to the front, and run like a cheetah on steroids without getting any of the food you really needed.