Last year, all flights at Christmas were a mess because of the weather. Delta was preemptively canceling flights left and right, so the airports got really ugly at times.
Normally, for a 12pm flight on Christmas day, the airport is bound to look about the same as any other day. However, as folks have stated, the amount of flights is actually less than normal, but the travellers tend to be more inexperienced. The nice part is that when you arrive at your destination at night, the airport will be dead. So, you'll be able to grab you bags and get out of the airport quickly.