a case of the 'don't know ya's
It’s when you know someone’s face inside out, but they act like they’ve never seen you in their life, probably because they’re a total brain-dead fool.
I saw my old math teacher at the mall and said hi. He looked at me like I had two heads.
At the grocery store, I saw my neighbor and said, 'Hey, remember me?' He said, 'Nope. Who are you?' Like I was a total stranger.
I saw my old friend at the park and said, 'Hey, it’s you!' He said, 'Who? I don’t know you.' Like I was a total brain-dead fool.