My parents dont believe me

My parents both say that it's okay to be bi or gay and they couldn't care less if my brother or I were, but when I try to tell them I'm bi they just laugh or say it's just a faze and I'm confused or dont know what I'm talking about. It's so aggravating! It's already hard enough because my brother is super homophobic and so is the rest of my family, but to have my parents lie about them not caring about it. I dated a girl for a year a bit ago and I had to hide her because I was worried my parents would flip out about it. When I originally told them I was bi, my mom laughed in my face and said "You can like the way a girl looks, but would you put IT in your mouth". It just makes me angry because no matter how I try to say it they just make a joke out of it and brush it off.