And some contradictions in the bible for good measures:
Some facts to bug the Christians around you with:
1) “Christmas" was long celebrated by the pagans around the world long before the existence of Jesus or Christianity. The celebration was in many names in different cultures for the occasion of winter solstice, an astronomic event marking the returning of daylight (longer day time) in the Northern hemisphere. The Chinese celebrate winter solstice without any religious connotation, usually on the 21st or 22nd, much like the early Greeks did, in account of their own calendar.
2) X comes from the Greek letter “x" (chi), and is the first letter of Χριστός, Christ in Greek. I bet most Christians do not know that.
3) Mary wasn’t always a virgin. She and Joseph were fruitful and multiplied. Jesus, provided he exited, had brothers and sisters, according to the bible. I bet most Christians do not know that either.
4) Jesus, had he existed, was most likely born between 6-4 BC, that is before Christ, not in AD, anno domini, meaning in the year of the lord. Modern historians largely ignore the distinction between BC and AD. They use BCE, before common era, and CE, common era, instead. No one has the slightest clue (since the bible is not a trusted historical source) as to the exact date Jesus was born on, by the way. Putting Christmas on Decembers 25 was most likely the early Church attempt to jump on the winter solstice bandwagon.