I'm a pretty polite guy, in guy, in person. Over the years, a few relatives have taken advantage of this politeness and got smart with me knowing I won't "make a scene" and do I wanted to do, which is to rub their idiot faces into a bowl of mashed potatoes.
After awhile, I finally asked myself why I continued to put up with them, especially considering I needed them for a grand total of nothing. So, I stopped dealing with family members on Thanksgiving and Christmas, and I couldn't be happier.
I'm not anti-family by any stretch. It's great if you get along with yours. If not, I see no reason to force it.