Knock! Knock!

For the third time this week, I have found myself in a single-person public restroom, door locked, conducting my business, when someone attempts to open the door, discovers it locked, and then knocks.

Who are these people?

When you encounter a restroom door that is locked, what goes through these moron's heads?

I wonder who is in there.
Maybe he will let me join him.
Perhaps he isn't aware that I am waiting.
Knocking is fun.

In response to these morons and their...