Based off Superman, it's the inability to notice that someone wearing glasses and that person not wearing glasses are the same person.
Kyle: Tim? Is that you?
Tim: Yeah.
Kyle: Oh. I almost didn't notice you with your glasses on.
Tim: Yep. That's Clark Kent Syndrome for you.
Tim: Yeah.
Kyle: Oh. I almost didn't notice you with your glasses on.
Tim: Yep. That's Clark Kent Syndrome for you.
by Rommer711 August 25, 2010