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

bonk/oif
 /bonk/, /oyf/, interj.

    In the U.S. MUD community, it has become traditional to express pique or
    censure by bonking the offending person. Convention holds that one should
    acknowledge a bonk by saying ?oif!? and there is a myth to the effect that
    failing to do so upsets the cosmic bonk/oif balance, causing much trouble
    in the universe. Some MUDs have implemented special commands for bonking
    and oifing. Note: in parts of the U.K. ?bonk? is a sexually loaded slang
    term; care is advised in transatlantic conversations (see boink).
    Commonwealth hackers report a similar convention involving the ?fish/bang?
    balance. See also talk mode.


The Free On-line Dictionary of Computing (30 December 2018):

bonk/oif

   /bonk/, /oyf/ In the MUD community, it has become
   traditional to express pique or censure by "bonking" the
   offending person.  Convention holds that one should
   acknowledge a bonk by saying "oif!" and there is a myth to the
   effect that failing to do so upsets the cosmic bonk/oif
   balance, causing much trouble in the universe.  Some MUDs have
   implemented special commands for bonking and oifing.

   [Jargon File]

   (1998-01-18)