Not exactly what you did, happened to me yesterday; I was bored and added funny things to my ticked, seems the GM was bored too. He came to us, popped Evil Big Chickens, had some fun. Gave us free beer too.
If you have a char on a low pop realm, GM's are usually pretty cool. Someone on populated reals too. I'll post a screen if I find it, but like 7-8 months ago ago during a raid in SSC (on Lurker) with my main char, there was a GM dressed in a pirate costume. Was funny, assisted us on the boss even!!!!! Well, nothing much, but he dps-d the boss with his rapier it was lulzy. It was kinda lame... because we wiped on that boss. Worse is we were at the time farming half of BT and cleaned Hyjal.