Replying to Closing doors to bathrooms when unoccupied

Here's my rant and you can take the poll if you like. I HATE it when you live/work with someone who has that habit of closing the bathroom door constantly when not in use. Obviously I'm talking like small one person bathrooms.

On one hand, sure if you take a smelly shit then it's not to stinky to the people walking by the bathroom, but then again it lingers longer so maybe it's just best to own it.

Otherwise
-I hate having to knock on a bathroom door to see if anyone is in there
-I hate having to answer a bathroom knock because I'm still taking a shit or piss, whatever
-I hate it when someone walks in on me going to the bathroom because I'm from the culture where a closed bathroom door means it's in use, so it's a hard habit for me to pick up locking the door (aside from being at work)
-I hate being mid piss or mid shit and remembering I didn't lock the door as I hear footsteps walk by the bathroom. Are they just gonna be barging on in?

Anyone ever had this dilemma? The struggle is fucking real.