..... because when you say "I'm on a diet," it puts far too much attention on yourself. When you really want to skip the junk food you're offered at parties and don't want that kind of attention on yourself, what do you say?
I actually have a valid reason that has ended up being a godsend for me... I have a lot of "almost" cavities, so if I really work hard at avoiding sweets, I might be able to heal them up. Also, any candy hurts my teeth immensely (as does dried fruit) because it is so sugary and sticks to it. I can have cake and ice cream and other such really soft foods, but things like chocolate and gummy bars cause me agony. So as a result, I can't really eat any candy. So when I get offered candy at a party, I can just tell people, "No thank you, I can't eat candy. My teeth aren't good and it is really painful for me" and they leave me right alone. If I'd said, "No thanks I'm on a diet," I have a feeling they'd ask things like "Why?" and "Oh come on, take some anyway," but once I turn it into a medical problem (which it really is), they leave me right alone. But it did occur to me that could just be a valid excuse in general. Like someone could say, "I have bad teeth and can only have sweets once in a blue moon so I won't get cavities" and you'd be able to indulge once in a while without question but most of the time could thwart people off.
For non-sweets, I often say, "I just ate" or "I'm saving room for dinner," etc. What about you guys? What are some of your tried and true "reasons" for declining food offered at social occasions?