@Moon one that has worked a lot is "will your boyfriend get mad if i ask you for your phone number?"

You find out right away if she has a boyfriend, and if she does, if she is willing to cheat on him, or she says he will be mad and you know that you are wasting your time to pursue it further, so you can move on to another girl. Pickup lines like this which are not really offensive, or corny but kind of humorous and let you know if you are wasting your time or not have always been the ones that have worked for me.