Yeah..if you say "no thanks" politely, and someone gets offended, then that's their problem..and why would it matter if you "offended" a person like that? Think like this for all your other problems with other people, and I gurantee you it will work as long as you don't do something wrong like stabbing someone with a pitchfork..
Just kidding LOL, but yeah.
Hmm yeah, sugar has no nutritional value...and it's not exactly good for you..but I think sugar in moderation is okay. My sister is a pharmacist and she says it's alright if you use splenda in moderation..like..1-2 packets a day. She didn't offer the explanation behind it though, I"ll ask her later if I can remember. But use stevia if you decide to use any artifiial sweetener, it's supposed to the best.
You could also get sugar free candy