I'm offended by the change to the thanksgiving menu because my so's guest is bringing something strange for the dinner.
Do you even know what they are bringing?
I heard you can't find it anywhere else. I think it's some kind of fish.
You may not understand why someone wants to eat a different kind of food, but not being open to trying a new culinary experience keeps your growth stunted. Welcome this person and their new dish in to your thanksgiving dinner and enjoy.
I'm offended by your approval and I think people should stick to the traditions.
But Thanksgiving is about celebrating the mixture of cultures. Cranberries came from the new world along with turkeys, and so these were all unfamiliar to the Pilgrims. It's fine for you to only eat what you like, but let your SO's guest share their own dishes if they like.