When I was five we moved into the house on Twenty-second Street in Richmond. In addition to the new house, the parents had purchased something rather spectacular -- a water pick.
This gadget was something that squirted a mildly-high pressure stream of water out of a plastic nozzle in-between your teeth -- hydraulic dental floss, if you will. And the first time I was messing around with it I noticed something. Since my parents had plugged it into the outlet that was on the base of the bathroom light socket, the water pick couldn't be used unless the light was on.
I turned off the bathroom light, filled the water pick's reservoir, placed the nozzle so it was pointing toward the bathroom door... and left.
I spent the rest of the evening waiting for the repercussions. I knew I was going to get it -- I just didn't know if the punishment was going to be worth the crime.
Nothing happened. My folks went to the bathroom and came out bland and splattered.
But when I went to the bathroom myself, as soon as I turned on the light I was spritzed. Hoist by my own petard. So the next time I went into the bathroom I didn't turn on the light -- instead, I reached across the room in the dark and fumbled at the water pick.
Sure enough, it was full, pointed at the door, and turned on.
Someone had refilled the pick since I set the trap the first time.
And that was how it was. We never discussed it, we never mentioned it -- but it came to be accepted that you turned off the water pick before you turned on the bathroom light, and that you kept the reservoir topped off. So people who were familiar with our house -- and we had a lot of guests, our place was a central party zone -- learned about the trap eventually but first timers were almost always nailed.
Again, this was never discussed, just accepted.
The water pick trap was in place, armed and ready, for thirteen years.
That's my family. We're all like that.