A description derived from the character Ebeneezer Scrooge in the Dickens novel A Christmas Carol. Traditionally a scrooge is a miser, pennypinching and obsessively possesive of their wealth, and totally devoid of any joy or compassion.
It is used especially in the context of Christmas, although it is now often used as a slur placed upon anyone who shows even the slighest reluctance to partake in the consumer orgy that takes up the larger part of the winter season.
As an aside, I personally have a deal of sympathy with the scrooges and misers, although perhaps that says more about me than I'd care to admit. Still, the whole Christmas thing feels so coldly mechanised these days I can't help but feel everybody is just going through the motions. I don't think it's entirely fair to hurl abuse at those who opt out of the madness - the last late-night shopping before the 25th is an experience I wouldn't wish on anyone.