just googled 'how to politely deny' and i think you're one of the first sites to come up!
My problem is with high school style, vague acquaintances - I want the words to say something more than 'no'.
"gee that's great you remember i was tall (e.g.)... i'm sorry though, I'm not comfortable sharing all my details with you." .. shouldn't you say something more than just deny? if not, they just request and request.