When I was a kid, I was given very clear instructions before birthdays and Christmas morning. My parents would always give me and my sister "the talk": The "no matter what you feel about the gift, say thank you and don't tell them if you don't like it" talk. It is so important for people of all ages to show gratitude towards their loved ones who have spent money on a gift for them.
That being said, you might not always want to extend that gratitude towards the company that you spend all of your waking hours grinding at. Getting a crappy coffee mug hits differently when it's coming from somebody you love versus a faceless entity you sell your labor to for survival.
Some female workers recently got duped out of a gift card after their male boss decided that an office Christmas party would be preferable, despite most of the office disagreeing. I think these ladies have a right to be Scrooges.