I tell my friend that I don't like the idea of calling me "best friend"
Why does best friend bother you so?
It's strange to me how people say "best friend" without "female/male" in it
That is an interesting thing to ponder on, and it's good you're speaking up about it. you need to tell people what's important and comfortable to you, otherwise you'll always feel awkward when they say such things to you.
But they know I'm a guy.
You should tell your friend if they make you uncomfortable. If they are really your friend, then they will respect the way that you are feeling.