The lock on my door doesn't work. (Like 90% of the locks in our house don't work) and if I did have one on my dad would be LIVID (even though I'm 18)
One time I put a note on my door asking my parents to knock before they came in because my dad always forgets and I'd been walked in on changing too many times and he got SO ANGRY
He started screaming about how this was his house and he could go wherever he wants when he wants to.
Honestly I deserve the privacy of that. I have RARELY ever done anything to not have their trust. They trust me to go out to all hours of the morning on the weekends (I don't do it often) so why can't I just ask them to knock on my door before they open it?