I'm going to ask my stepson to give a courtesy knock before he walks into the bathroom.
Why does he need to knock?
He does weird things so I don't want him to get his hands on dangerous things like the toilet cleaner so I need time to put it away.
While he is a kid, it is good for him to understand that he needs to respect other peoples things. Otherwise people won't want him around.
I want him to respect my privacy so I ask him to knock.
Its only right to get this done this way. Your things are not to be toyed with, especially toilet brushes which can harbor a ton of germs.