How to politely ask a girl to wax her mustache?

Ask her if there is something about you physically that she does not quite like and that you could change to look better for her. If she says no, ask really, are you sure, if she insists that there is nothing, smile. She may ask if there is something that you do not quite like about her and would like to change. Then tell her how beautiful you think she is first, then come out and tell her that you think if she would wax her upper lip it would look better. If she is offended then you lost her but then it seems important enough to you to take that chance, right?