Haha, I've never toked up in the bathroom. Its not a very strategical place in my house, in my opinion. I just wait till my parents are asleep and chief in my room while blowing the smoke out the window, I don't expect them to come in my room since they're asleep, so I'm usually good, sometimes I have not even bothered to open the window. But it can get smokey, so its better too, plus sometimes you can smell it in the hall, and you need to pass my room to go to the other parts of the house.

Best way to not get caught: Don't be high around your parents at all, and only smoke when they aren't home. Night time toking can even be dangerous, even if its midnight. I know from experience.