I'm trying to figure out what is wrong with knocking on a door before trying to open it? We do it at our school all the time - sometimes the 'occupied' sign is broken, as in, one of our bathrooms has it stuck on 'occupied' all the time, and another one on a different floor doesn't have the indicator at all. We all knock before we open the door - sometimes people forget to lock the door if they are in a hurry (oops!) and it would expose the occupant to an entire hallway of students.
I think people are being polite when they knock. They could just pull on the door, and if you forgot to lock it, well, then...
the issue isn't one polite knock. I don't think anyone would think that or discretely trying the door is an issue.
But, it's not usually one polite knock.
The issue is that during a few minutes in the restroom, there are usually repeated knocks and not just knocks, but poundings. Sometimes they start when we have barely closed the door and continue until we get out.
When someone knocks, I will usually say I am in with someone who is disabled and I expect to be x number of minutes more.
I know the people hear me, because some comment back to me. Most of those are of the 'nice' type - "I didn't know if anyone was in there....take as much time as you need.....that's ok. We'll go in the other restroom."
I can also hear their comments to each other. Sometimes those are if the distinctly 'not nice' type - "well, just keep knocking until she comes out...that's ridiculous to take that long....[to a guy] can't you take him with you to the men's room?" And the guy's response, "I don't want to. Just keep knocking to hurry her up. We're wasting time."
And a woman to her child "kick the door." The last one kept egging her child on for the whole time we were in there. Every time he stopped I could hear her tell him to start kicking in again. When we came out she blamed him for it and said he was very impatient and was a bad boy.
Every 30 seconds - come on now.
That's the kind of annoying knocking that I am thinking of.
It's bad enough at times that at some parks we don't even try to use the Companion Restroom unless my DH is with and can monitor the door for us.