For a very long time, we didn't have lock on our bedroom door. In fact, the knob was so completely broken, we couldn't even shut it properly. I would put a laundry basket in front of it in order to keep it shut.
And my kids don't knock.
So, one day I was innocently changing my clothes. One of my boys comes in as I was facing the door. He immediately covered his face, turned and ran screaming out of the room.
He was screaming, Ahhhh Ahhhh! I just saw mom naked. My eyes, my eyes!
I overhead his brother say to him, "Ooohhhhh THAT'LL give you P.T.S.D.
Good news is that, thanks to my father-in-law, we have since put new doors in with LOCKS! So no more trauma for my kids.