Some play an instrument like the piano or trumpet. After they play one song they know it by heart. They are often kind people when you talk to them, but you mess up a song and they will go ballistic. They wear over sized glasses or just plain glasses and are always out of style.
Guy: "Yeah I saw him and he's a music nerd, I mean look at those glasses."
Girl: " I guess he is nerdy with those glasses on."