To be in a mood where you want to sit in a corner and die! Comes from the fact that when you corner a Giraffe and threaten it, it lies down on the floor, closes it's eyes, and dies!
If you are Giraffing or Giraffed, you just cannot be bothered, no matter what the situation!
Hung over after a big night out and a mate wakes you up at 7am to ask you to help clear up;
'I'm so badly Giraffing (draffin') bro!'