a word William Sledd (a youtube star) created with his friend Lindsay.
There is no excact definition, William Sledd defined it as " i dont know what it means, but it sounds a lot better then christmas!" :P
I think bitchmas means something like christmas just with green christmas hats. from victoria secret.
Bitchmas colors are pink and green,
and Santa Clause is called "my bitch"
watch link for the video, remove the stars.
"Merry Bitchmas Bitches"