Looking For the Origin of 'BirThankMas'

'BirThankMas' is a combination of the words 'birthday', 'Thanksgiving' and 'Christmas'. It names an ad-hoc holiday in which one combines the three events for the honor of one person. For example, let's say my sister and her husband were born about the same day, and I have not visited them for Christmas or Thanksgiving in a long time. My wife and I might take them to dinner and a show for their BirThankMas present.

I don't know the origin of this, but I know I did not make it up. I believe I heard of it in a movie or a television show. If you know the origin of the word, please post a response here.