Quoting Jax.:" Best quote ever! "Gender is who you go to bed as," he says. "Sexuality is who you go to bed with.""
I prefer the term "Gender is between the ears, sex is between the legs." Its more so a term as gender is who you feel in the brain, sex is what your identifying sexual organs are. Though, if you are transgender you will not match that saying fully, but if they were to have a sex change it would.
I taught my students gender and sex in poetry and I had them remember the between the ears/legs part in order to understand the poetry we listened to. Someone else mentioned the part of bisexuality which is why the "who you go to bed with" doesn't fit fully. So the "My gender is female but my sex is male" makes more sense because between the ears, they are female, but the girl has male sexual organs.
Does that make sense?