In my experience, telling people to fuck off is the most effective way to convey the message that you wish that they would fuck off. Sounds to me like you're just a pussy. You don't need to send a message to your parents that you are a responsible adult- it is self evident that your life is not theirs to do with as they wish. If it is not something they are willing to recognize, you have to take a firmer route.
Why on EARTH would you want to strengthen a relationship with someone who meddles in your affairs? You are the tardiest of tards. Since today is the fourth of July, I'll go ahead and say that if you were running things in 1775, the U.S. would still be a subject of the british empire, because you are a tardy fucktarded pussy.
So fuck off.