It is no news that boys and girls aren’t raised the same.
Little girls are often told to “clean up” and “act like a lady.”
It is known that sitting with your legs crossed is considered ladylike.

Such a position is oftentimes described as butch and usually leads to the woman being characterized as unfeminine.
“Sitting pretty” is one of those things.
Crossing your legs can actually weaken your pelvic floor.

This can cause a variety of problems; the most common are issues with your bladder and bowel functions.
Still, more serious health issues like these will not arise just because of your sitting posture.
How to sit better, not pretty
Replying to @roorooroo yes they do!
even if you feel comfortable when crossing your legs, I do not recommend it doing it too often.
Bad body posture can evenaffect your skin, and you don’t want that.
It’s time to ditch leg crossing when sitting.
Don’t “sit pretty” your pelvic floor will thank you.