Haven't really had this problem since high school. And even then it was mostly her asking her friend to ask me.. blah blah blah. Only once did i have to actually deal face to face. I basically told her that as a Christian i couldn't really date her since she wasn't a Christian... she tried telling me she was, actually a mormon i believe. But not a practicing one, thats for sure haha. So then i had to point to her smoking, drinking and drug use. Fortunately that worked.
Now its mostly me picking up on someone having an attraction to me. Once i get that sense i try to do things to discourage it. Keep a distance from them, maybe try to highlight some of my more negative aspects, haha. There's ways to stop them haha.