LoL friendzone him. "your like a brother to me" "your my best FRIEND" theres many ways to tell him to **** off >.>
Or just tell him your gay. he wont even bother with you.
may be a bit harsh how i say it but thats litterally what happens in real life. all the time. wether you want to notice it or not.
Be polite and just say you'd rather not have a romantic relationship. It's simple.
Immediately change the subject, and keep going.
tell them your considering changing gender :)
You tell him "I'm truly flattered that you feel this way towards me, but I'm not diggin you like that. You're a cool guy, but I'm not interested."
just explain why not with more details
Just say "Sorry, I'm not interested in you"