Here is the Merriam-Webster definition of mundane:http://www.merriam-webster.com/dictionary/mundane
I did not mean it in any pejorative sense, nor was I making fun of anyone. It is, in my mind, a shorthand way of referring to non-fans. And, as VorFemme said, it can be applied to many different areas.
In fact, as far as some genres are concerned, I would classify myself as mundane. I love Ren Faires, I do respect and admire the SCA (the incredible attention to detail of the garb, the rank structure, the general intensity of participation), but I am not a participant. Therefore, I class myself as mundane in the SCA world.
Also, in the areas of vampires, witches, werewolves, and Xanth (I do love Anthony's Incarnations of Immortality series, though, except for the book about Nox) I would be a mundane.
However, in the world of Heinlein, Asimov, Clarke, Babylon 5, some Star Trek, Star Wars, Silver Age DC, and Spider Robinson (to name a few) I am a dyed-in-the-wool fan!