Ways I successfully avoid the social awkwardness you mentioned: 1) If present with an SO, say you are sharing theirs. 2) Take the proffered sugar, make eating

Ways I successfully avoid the social awkwardness you mentioned: 1) If present with an SO, say you are sharing theirs. 2) Take the proffered sugar, make eating-cadence motions with the spoon/fork but instead of eating, mash it a bit. After a few times, hard to tell at a glance whether or not someone has eaten it. Discreetly set down, walk away. 3) Or do the more advanced version, when you realize rarely does someone really observe and care that you eat a food, and being seen in the give-and-take transaction with you is far more socially significant: take, dab with utensil, discard. 4) Decline with a wry "doctor's orders". YMMV, might be accompanied by increased risk of one-sided conversation over health issues, especially if giver is elderly relation with lots of such.