How do i convince my parents to let me be what i want to be?

I've drawn a lot ever since i was lille. In elementary school me and my friends used to make "comic books" (even though i'd never even read a comic before lol). In sixth grade one of my friends got me interested in manga (japanese comic). I started to read manga every day and i came up with my own stories and characters and stuff. In seventh grade i decided that i wanted to be a mangaka (japanese comic artist) when i grew up. But whenever i buy manga my parents think that its a waste of money and tell me to stop buying them. My dad also teases me (in an EXTREMELY annoying way) and says that all i watch is "japanese shows", even though that's not true (He thought Ben 10: Ultimate alien was japanese lol). Whenever my parents asked me what i wanted to be, i lied and said " architect" but now whenever they ask, i say " idk". At the beginning of the year i started reading american comics and decided that i want to make comics here in america. But i still tell my parents that idk what i want to be because they think that artists are all poor and that you can only get good jobs if you're good at math and science (and i hate both of those subjects). They want to be a doctor or a lawyer or something. It's funny cuz they used to say you can be whatever you want to be, but now they say be what we tell you to be. My mom says that this summer she's gonna buy a book of careers and wants me to choose one, but i don't want to waste her money since i already know what i want to be. How do i tell them that i want to be a comic artist and convince them to let me do it? If you can't think of a way help me convince them, what are some ways to bluff about what i want to be. Sorry for boring you with my life story but I really need help.