(Just for the sake of fun)... You go to the undead ghost sailors on the sunken ships off the western coast of the Wetlands. They can cast a spell upon your pet that will turn it into a forsaken ghost.. male or female. This is how you determine what gender WoW considers your pet to be. (FYI: The easiest way for high levels to do this is to put your pet on passive and send him or her in to stand on top of a sailor so that it aggros and isn't one shotted by you or your pet).
I admit, I am a bit curious; but at the same time I'm afraid that I might find out that Pyrotess's cat, Isis, is a male (as I’ve been role-playing the exact opposite).

Oh, and warlocks.. this works on your 'pets' too. *winks*
If anyone wants to gives this a try, post here and let me know your results!