My favorite instance of emergent mailing list behavior was when a trouble maker named GUMBY created a "PLEASE-REMOVE-ME" mailing list, just for people who sent email to another entire mailing list asking to be removed from it, instead of sending their request to the administrator at mailing-list-name-REQUEST.

Whenever somebody would make that faux-pas, he'd add them to the PLEASE-REMOVE-ME mailing list, and the emergent behavior was that those people would discuss amongst themselves the fact that they really wanted to be removed from the PLEASE-REMOVE-ME mailing list, until they eventually learned that the way to get removed from a mailing list was to simply send email to PLEASE-REMOVE-ME-REQUEST, instead of the entire mailing list.

Worked like a charm!