Used to describe the after-effect of Christmas, or the Holidays in general: 12 Days of Hanukkah/Christmas, etc. is usually a busy time, very exciting, and enjoyable. By the end of the celebrations (The night of Christmas Day/Dec. 26th) you feel exhausted and overwhelmed. People are usually groggy, lethargic, and almost depressed from exhaustion.
I love Christmas. But all the celebrating, visiting with family, and celebrating...I'm Christmas Crashing
Joe 1: What are you doing for New Years?
Joe 2: I'll be in rehab.
Joe 1: Why?
Joe 2: I'm Christmas Crashing hard this year. The idea of going out for a drive is exhausting.
WoW Weight refers to the weight you put on after excessive/prolonged periods of playing WoW; recently speaking, WoW: Cataclysm.
It's also what you would say after realizing you put on the weight; ie "WOW," due to the fact you put on so much weight from playing.
Joe: looks in mirror
Holy balls! Wow!
Joe 2: What is it?
Joe: I've put on a lot of weight, geez.
Joe 2: You bought Cataclysm, right?
Joe: Yeah, so?
Joe 2: WoW weight, gg.
Jim: Man you've got a lot of food. What for?
Jim 2: Just bought Cataclysm, gonna put on some Wow Weight.