I don't want to take part in the office Yankee swap.
Why don't you want to participate in the office Yankee swap?
I don't like taking part in things which I'm not interested in. I don't even really know what Yankee swap is.
I understand why you might not want to take part, but it's good for the morale of your coworkers if you take part in it. I think you should ask them what Yankee swap is all about, and try to have fun.
Nah, I still don't want to. I should do what I want and stay where I'm comfortable.
It will be awkward if everyone does it and you don't. You can learn what it is and it might be a lot of fun.