I’ve been told this too many times to count. Along with: 

“You have lady parts, therefore you’re a girl.” 
“No, I will not use male pronouns.”
“But you’re such a pretty girl.”
“Wow, shave your legs!” 
“If you were meant to be a boy, God would have made you one.”
“You look ugly without makeup though.” 
“I’d date you if you had a dick.”
and my personal favorite:
“You need to get your head checked…”