How I get over the guilt when exchanging or donating unwanted gifts

As an adult I find that I have a lot of guilty feelings over receiving gifts that I don't actually want, need, or like. Whenever I receive something that I don't really want, need, or like I revert to the my polite seven year old self — I smile and say thank you.

But now it's more complicated as I'm the adult who has to decide what to do with the unwanted thing…