Come to the Dark Side... We Have Santa!

Dear readers, we all have a bit o' evil in us. Some use their evil to rob banks and hurt kittens, but others, who are creative in their vindictive actions, use their evil for the betterment of all.
Case and Point, each year at Christmastime,I excitedly exclaim my belief in Santa to my two Christian-raised nieces. The nieces will politely (but firmly) refute, saying "there isn't a Santa Clause; he's not real."
And this is when I have the opportunity to undo their indoctrination and instill a modicum of Skepticism.
"How do you know?" I inquire.
And that's when the fun starts! Back and forth, every well-intentioned Apologetic that has been hurtled at me can just as well be used to "prove" Santa is real.
The nieces are still young and isolated in their world views, but as Santa as my witness, I will deconvert them yet!
(Unless they attend a single science class... that'll work too.)