By the time you reach adulthood, I would think that you would have acquired some basic pleasantries that can be, if not used everyday, at least trotted out for special occasions. Things like "no, I wasn't watching that show, go ahead and change the channel" or "I love that color on you" or "that's ok, you can have the last bite of cheesecake". At a minimum you should know how to respond appropriately when someone gives you a gift. If you love it, it's easy to say "Best Gift Ever!!!" But even if you momentarily go blind opening that horrid puce sweater/socks/afghan set Aunt Ethel back in Baltimore knitted you, how difficult is it to say "Thank you for thinking of me. It was very thoughtful". It's called The Receiving of Gifts Etiquette, and frankly, some people suck at it.
I read a book this summer that I really, really enjoyed and immediately bought several copies to give as Christmas gifts to friends/family members who are always on the lookout for a good read. Imagine my surprise, then, when one person (let's call her my boss) emailed me to say that judging from the cover the book doesn't appear to be anything she would like, and oh, by the way, if I ever send her a book again, would I send it to her electronically as she likes to read on her Kindle.
I realize that everyone's tastes are different and not everyone will appreciate what I have chosen for them. I am ok with that because the reverse is also true. I have gotten things I have truly wondered what on earth the giver had in mind when he/she bought it, or how many times has this been re-gifted to end up with my name on it, or where am I going to stash this until Aunt Ethel visits. But for all the sometimes weird/ugly/unwanted gifts I have gotten, I can't imagine any response other than "Thank you, this is very thoughtful". Because I am an adult with adult words and adult sensitivities. For all my faults, and I am sure they are legion, I truly cannot conceive of telling someone I don't think I will like this gift, next time try to do better. How about next time I don't give you a gift at all, how does that work for you?
But of course I will because of the whole being an adult thing. Whether it be the candle my boss gave me this year that looks exactly like the one she gave me last year, or something I gave my mom 2 years ago that she had forgotten came from me and has now wrapped and given back to me (yes, she really does that), I will say "Thank you, this is very thoughtful".
Growing up is easy, sometimes being an adult is tough.