free dessert dilemma

Iam trying not to eat desserts/sugary items (in fact, I hadn't had any at all until March). I am not diabetic or anything, but I am trying to avoid wrinkles, weight gain, etc.
Here's the problem: What do you do if you go to a restaurant and they send you out a free dessert, just because you're a good customer?
Of course, in my quest to be unfailingly polite, I eat the dessert (but then get mad at myself).
Is there anything else to do besides be thankful that they appreciate my business, and eat the treat?

I wouldn't feel bad about taking a couple of bites...try and pawn the rest off on your dining partners....

Eat and enjoy. Eatting a dessert every once in a while isn't going to make you fat. Don't bother getting mad at yourself, you're likely to cause yourself greater harm through the mental stress over failing to adhere to an overly rigid diet than you are to get fat or wrinkles from the rare dessert you are going to be gifted.

It's certainly understandable to want to restrict sugar in your diet for health reasons, but as long as you aren't downing sodas, candy and sugary treats every day, you'll be fine. The odd dessert when out to dinner isn't going to affect you.