Not to be confused with Trekkies (though often the Fantasy and Sci-Fi interests overlap).
(Could be considered by some a variation or specialized form of the terms Nerd and/or Fanboy, but 'Rennies' is not inherently a derisive or pejorative term. In fact, Ren Fair participants generally call themselves "Rennies"; they are not called "Rennies" by outsiders.)
I don't need to imagine it. It already exists. It's called "THE INTERNET".