You shouldn't call mentally challenged people losers.
A mentally challenged man stopped Jeff on the sidewalk and wanted to have a conversation.
Jeff wants to get away from the man.
Jeff tells the man that he's late for an appointment.
Jeff tells the man to get away from him and calls him a loser.
The man doesn't want to bother Jeff, so he leaves him alone.
The man's feelings are hurt, and he doesn't understand what he did wrong.