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

net.police
 /net?p@?lees'/, n.

    (var.: net.cops) Those Usenet readers who feel it is their responsibility
    to pounce on and flame any posting which they regard as offensive or in
    violation of their understanding of netiquette. Generally used
    sarcastically or pejoratively. Also spelled ?net police?. See also net.-,
    code police.


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

net.police

   /net-p*-lees'/ (Or "net police", "net.cops") Those Usenet
   readers who feel it is their responsibility to pounce on and
   flame any posting which they regard as offensive or in
   violation of their understanding of netiquette.  Generally
   used sarcastically or pejoratively.

   See also net.-, code police.

   [Jargon File]