To wear glasses that you don't need, or different clothes than you normally do in order to obscure your true identity. So called for Superman's alter ego Clark Kent, who by the simple act of wearing glasses and a tie was somehow able to avoid people realizing they were the same person.
"Take a look at John, he's totally Clark Kenting it to impress that Jessica chick from his econ class."
"What do you mean?"
"He doesn't need glasses, that dude has 20/20 vision. He's just trying to look intelligent so she'll like him."