You Dropped Something!

This trick is more for teenagers, but I suppose it culd work with other people with a few variations. When you go to talk to the person you're flirting with, hold a note written between two friends about how attractive that person is, etc. Then as you're talking, put it down out of his view. Then walk off, leaving the note behind. Try to get away quickly. Hopefully, the 'flirtee' will find the note and read it, revealing the crush!