Heh.. my mom knows. It's kind of a weird case, since I stumbled upon the whole thing through a fan site for a movie I'd seen as a kid. She was a conservative Christian then, so I hid the fact I was MUCKing for a while. She found out, though, and after hearing the why's of me chatting and roleplaying online, she started becoming less and less conservative. Now she knows a lot about it. She even helped me make my first fursuit.
My dad's another story though. I introduced him to the muck I used to run, once, and one night he connected and made a complete fool of himself (And I don't mean flaming or what have you. I mean literally acting like an idiot.). So he doesn't know anything further than that, though he does view my deviant art gallery from time to time. He's not very bright, so even if I flat out told him, he wouldn't understand enough of it to really have a reaction.
