Ideas on how to talk to my father?

I’m 19, he’s almost 70. I’m the only girl. Ever since I became a teenager he’s always yelled at me to sit like a lady, sit with my legs closed, etc etc. Of course I’m perfectly appropriate when I’m wearing skirts/dresses, but I’ll be wearing jeans and sitting with my legs crossed or open (like guys do) and he gets upset. I’m not really sure how to broach the topic with him, but I am getting quite frustrated because nowadays at least it’s perfectly fine for women wearing pants to sit with their legs open but he seems to think people will think I’m easy.

Note: none of these are ridiculous poses, I’ll just be sitting in bed or eating while reading a book and he’ll come in and yell at me for not having my legs shut