Here's a good one...
I learned this at a conference and it worked REALLY well. By leading the class through the process, they 'police' the bathroom by themselves and I don't need to chime in at all w/ reminders.
*When my class moved from our temporary bldg. to our new one, with a bathroom located in our room, we had quite a few 'surprise' door openings, etc.
The kids and I charted:
What is important about using the bathroom?
I wrote down everything they came up with. All of it child-driven and very on target. (there were about 8 things)
We reviewed the rules and I made a stop/go sign with the whole group to place on the door.
After about a week+ I said 'there are too many words on this chart. Let's see if we can make it easier to read'. We condensed it down to 4 rules and I took pictures of each (knock-hand knocking, flush/handle, etc and very brain compatible).
I posted the chart on the bathroom door and the best part...THEY FOLLOW IT and if somebody doesn't, they take care of it.