The other night I was in the bathroom, and my 8 year old son came abruptly to the door. "Are you on the toilet? Are you going to be done soon? I need to go now."
When I told him that I was going to be a while and that he could go upstairs, he sighed loudly enough to be heard through the door, and then pounded up the stairs. A while later, after we were both out of our respective bathrooms, I commented on how it was a good thing that we had two bathrooms (well, actually 1 1/2, but it's the number of toilets that are important). I told him that when his dad was growing up, he had a brother and a sister, and their whole house only had one bathroom, and everyone had to wait if someone else was using the bathroom.
"Yeah, and their one bathroom was even outside," my son replied. I had to explain that Daddy wasn't that old, and I didn't think that anyone still used outhouses in suburban Chicago in the 1960's and 1970's.