Haha, 'John'? Seriously?! :P

Let's see...
throne, potty, latrine, outhouse, netty...

Can't think of any other at the moment.

Well, a lot of those are synonyms for the place containing the toilet, rather than the toilet itself. So I suggest it's two lists, one for the room, one for the appliance. They're differentiated by usage, among other things: one is IN the room, one is ON the appliance. For instance, if someone says "Hey, where are you?" You'd say "I'm in the little girl's room!" or "I'm on the crapper!" as appropriate.

Room: bathroom, water closet (also W.C.), the head, restroom, little girls' room, little boys' room, ladies', men's room, ladies' room, the john, the jakes, powder room, lavatory, outhouse, bio breakroom, the library, lav, dunny, long drop, kybo, biffy

appliance: toilet, potty, latrine, crapper, porcelain god, the bowl, s***ter, p*** shelf, can, commode, stool, chamber pot, throne