Isn't it amazing how someone who essentially is a guest in your home can lose their manners.....and think it's ok......
Let's face it. Once a person turns 18....they are a guest in their parent's home. They no longer really "live" there and a parent is no longer (legally or otherwise) required to provide housing for them. The burden of being accommodating to the "house rules" lies with them......not with the owner of the home.
Say what you mean (set your boundaries), mean what you say (those boundaries are NOT negotiable) and don't say it mean.
gentle hugs
ke