L-R checker
a person who yells at you if you put the wrong earphone in the wrong ear
I told you to put the L in the left ear, but you put it in the right and now I'm deaf in one ear.
My friend is the L-R checker and he screamed at me for 10 minutes because I mixed them up.
At the concert, the L-R checker got so mad he kicked the sound guy.
xs