The Jargon File (version 4.4.7, 29 Dec 2003):

pred
 //

    [Usenet; orig. fr. the Island MUD via Oxford University] Abbreviation for ?
    predictable?, used to signify or preempt responses that are extremely
    predictable but have to be filled in for the sake of form (the phrase is
    bracketed by ...). X-Pred headers in mail or news serve the
    same end. Figuring out the connection between the X-Pred tagline and the
    thread is part of the entertainment. For example, it is said that any
    thread about taxation must contain a reference to Raquel Welch, if only to
    stop other people from mentioning her. This is allegedly due to a Monty
    Python sketch where a character declares that he would tax Raquel Welch,
    and he has a feeling she would tax him.