In other words, the user is an idiot.
Helpdesk "What seems to be the issue?"
Caller "It doesn't work"
Helpdesk "Could you be more specific"
Caller "I've tried everything and it won't let me in"
Helpdesk "I think there's a PBKC. Have you tried turning it off and on?"
Used to describe the source of an (computer) error. P.B.K.C or PBKC means the eror is a human or operator error and not a hardware or software error.
PBKC is an alternative version of the definition RTFM.