A more modern and less courteous way of saying Bah humbug. A phrase used to show disdain, disinterest, frustration or general irritation with the holiday season. When you can't stand being around insane crowds, bad drivers, fake cheeriness and stupidly decorated houses any more, just yell it at everyone.
Cratchit: Hey neighbor! Have some Christmas cookies! Merry Christmas!
Scrooge: Your wife's cookies suck, your house looks like the holidays vomited on it, and I don't like your family. Chrismyass.