Why won't my parents let me get a face tattoo?

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So i want to get my boyfriends last name above my eyes stretching across my eyelids with a heart after it and my parents told me no. I mean I'm 13 now and I've been dating him for like a month and a half. I feel that I'm old enough to make my own decisions about my body and make life choices. I smoke weed and drink all the time so I'm basically and adult. My boyfriends supports me 100% except my parents don't like him. I met him on facebook and we chat on there every night. I wish my parents would stop being so controlling. They bother me so much. They always yell at me too. One day i came home smelling like pot and my parents decided to ground for the whole week for no reason at all! I feel I am in a serious relationship and my bf said I can move into his house when i turn 17. I know I'm much smarter than everyone in my family and they're honestly so stupid. They just don't understand what TRUE love is. What do I do. How do I tell get my parents to let me get my tattoo. Should i just get it from the kid at school and not tell them. PLZ helpz.
I was also thinking about getting a teardrop because my boo told me everyone would think i was cool. I mean lil wayne has one and he is such a good influence and rapper.
For the people who say smoking weed is bad they are stupid because its actually really good for you. Weed is a plant and plants are good for you. Why else would people eat salad, stupid? My friends tell me that weed can actually make you smarter you just need to smoke alot of it. Thats why I've been smoking a bunch when I study at my friends house. I even have been smoking it in between classes in the bathroom. It hasn't made any positive changes but my friend just said I need to smoke more.
My bf says he really loves me and really cares for even though he doesn't live at his parents right now because of similar reasons I know he will care for me. He even has been looking for jobs at taco bell and speedway so that he can support me and maybe our future children. I'm not pregnant yet but i really want one and I know i could be a good mother.