Just be honest, tell him " I can tell you are interesed in me, but I have to be honest with you. I am just not interested in you in that kind of way" Or something similar. No need to cut him to pieces, but just tell him bluntly the truth. Nobody likes to be rejected, but it will only be worse for him later. Don't let him keep flirting with you because he will really feel foolish later on. my 2 cents....
Seriously? Dude, I love the fairy cup reference, I'm so stealing it. Maybe I'll make it popular in Canada, hehehehe. er.. hey, I have to amuse myself somehow don't I?