Strict household?

Okay so my parents supposedly lead a “sex positive/ open household” but when when is girls (my sister and I) make jokes about sex or talk about sex, we get in trouble, but when my brother wants to talk about sex or joke about it it’s perfectly fine? I could understand why they might be upset about my sister talking about cause she’s 15, but I’m almost 18? Anyone else have this problem? It’s like they think that just because we talk about that we just go sleep around behind their backs.