A "rare" anxiety disorder that typically starts in childhood. It's main trait is being mute in public. But this trait can extend to nonverbal communication as well. Basically social anxiety on drugs.
Child: *has selective mutism*
Parents: Our kid is rude for not talking in public so instead of taking them to therapy let's leave them like this and continue to be upset at them because it must be a choice cause children LOVE not having friends! Lol!