What are some of society's rules based on race, gender or other differences between people that you don't understand?

I don't understand why it is ok for a girl to call a guy a dick but a guy can't call a girl a cunt. I don't like the word cunt, but they're analogous. A cunt is slang for a girl's genital region while dick is slang for a guy's genital region. My mom said that it is because girls, in the sense of being ladies, shouldn't be called names, but then ladies wouldn't call men names either.