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It was the "the funniest, sexiest newsgroup in the world." 
A fan in 2015 said: "i think ratmm remains to this day one of my finest fandom experiences; i am so sad i don’t have my massive carefully curated saved folder of MSTings anymore. that was such a glorious art form" 
Rec.arts.tv.mst3k was the predecessor to RATMM.
Okay, first things first. If you don't know what MST3K is, a) I pity you, and b) you can find out all about it here. Now, assuming you have that down, I can explain that RATMM is the official MST3K newsgroup, and it's the only place on Usenet that I feel a real affinity for, for reasons that are only slightly relevant to MST3K itself. That is, the show gets talked about there sometimes, but much like the Spider Robinson Usenet group alt.callahans, the newsgroup has completely (d)evolved to a free-for-all discussion on anything and everything. It is, however, informed by the sarcastic, silly mentality of the show itself, and also spiked with a good bit of nonsense and flirting. I have a real affinity for this place - I met at least half a dozen of my closest friends there, and at least one love affair resulted from it. So I LIKE IT VERY MUCH. I am now and forever known there as The Midnight Rambler, which sort of has something to do with the Stones song, but not really, so it fits. 
Stephen Cooke | Mike Barklage | Jim Ellwanger | Chris Cornell a.k.a MSampo | Brian Henry a.k.a Erhardt4 | Aron Craig a.k.a Jello | Norb|Chris Gleason | Doug Barkes | Jungle Goddess | Noah | Brandy | Pat Flanagan | Soundwave a.k.a. Chad Gould | Julia | Tarpo a.k.a. Robert Tilley | Col Di a.k.a. Diane Thorne | Faye C Schuss | Mike Czaplinski | Mike Ralls | Catherine Johnson a.k.a. TCurryFan |CLMoon | Hilary Doda the Queen of Sin | Big Rob the Midnight Rambler | Mike Grasso | David Anderson aka lando5 | Roland Warner | Steven Thorpe a.k.a. thor | Carol Bourgeois and Company | Roger M. Wilcox | "The" Sheryl Gere | Laurelyn "Anagram Princess" Smith | Sarah Heiner a.k.a. bookworm | Sascha | creepygirl | Rick Thorne | Andrew 'Retro-Man' Morris | Jeanetta Adkins a.k.a. sharkbait | Nummy Muffin Coocol Jolene | Tom "FoxTrot" Cox | "Average Joe" Barlow | Nicklby | Matt "Pinwiz" Elcock | Bart Fargo |Booga | Angela a.k.a. ACMCE | Kevin "Professor Bobo" Mowery | Kenneth Kubik | Todd "Toddster" Johnson | Ruth McIlhenny | Bryan Lambert | Tom R | Jess | Ian W. Hill | Evan | Bob "Bice" Eichler | B.G. AKA WereTorgo | David J. Ramirez | Diana Deacon, the Humble Acolyte | Heather "Magic Voice" Holder | Joe B | Michael K. Neylon| Skins | Reaper G | ShadowStar aka Joe Earles | K-Y Mellie | Christine ~ aka Tilde, the Beloved | Jules | Lori Holuta | Michael Clear | OdiePal | Brian Pacula | Erin Evans | Adam Schillinger | Alia Robinson | Robert Hutchinson | EvilJen