Problem Between Keyboard and Chair (Problem Between Keyboard & Chair).
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.
The user who called the help desk thought that the system was down, but it was just a p.b.k.c error.