Is it possible to have a Happy Fat Christmas? Sure it is.
One tells people who are concern trolling -people who seem to have our best interests at heart, but somehow end up criticizing our bodies- that Santa Claus and Mrs. Claus are hot, and that they obviously have found exercise that suits them. Another thing one might do and say is jump up and down and sing "Bounce Your Boobies", which will drive anyone away whom you don't know too well.
Tell someone who asks if you've lost weight that you now have a magnetic cellphone app that can locate your weight and put it back if it gets lost. Tell someone who asks if you've gained weight that you're training for the lifting marathon and lift that person up as high as you can.
Tell anyone who asks that red is a fat and beautiful color and that is why you're wearing it.