Peeing in bf mouth

My boyfriend has been mentioning things basically insinuating he wants me to pee in his mouth. I wouldn’t mind doing it I think it’ll be sexy. My thing is should I randomly do it when he’s eating me out or should I ask him before I do it lol smh 🤦🏻‍♀️ Sounds weird me even typing this but how would I even say it ?? & yes this is a serious post & please no rude comments.