THIS. Basic politeness is so underrated. I mean, people are NOT going to be upset if you ask to speak to them, if they say no then ok problem solved you can walk away. If they say yes then they won't be upset with you respectfully telling them you think they're attractive. (Bonus points for complimenting something other than a body part like a fashion choice or a hairstyle, makeup etc. because these things display more of a person's personality and complimenting them shows interest in that).