Why does he act interested yet avoid me sometimes?

He's done everything to show interest, and I know for a fact he is not that big of a flirt. I feel like people notice it too, yet he'll act cold sometimes. He pretty much ignores me on Facebook, yet bothers me a lot in person. He's sending mixed signals and I thought I made it clear I was interested, so either I'm more subtle than I thought or he's really not interested. Can anyone explain this?

Always more answers are appreciated! Thanks!

**Specifically if you are a shy guy, but more so one who is shy yet acts like the class clown a lot, so that it appears you really aren't shy at all.**