I'm of the opinion that you should respect your parents, but if they are going to take you shaving your head as disrespect then they are worrying about the wrong things and should be glad that's all you're doing. I'm sleeved up with tattoos and my parents hate it, but have to accept it because it is who I am. I have been an otherwise obedient child and always respected them, and worked hard to earn theirs, so my choice of appearance is not their concern. If you can say the same, then whether they approve or not, it isn't their call.