A "hood up day" is a phrase used to describe any day for which:
One's physiological state is less than preferable
AND the course of action taken to rectify this situation is to conduct the daily routine in a hooded sweatshirt with the hood of the aforementioned sweatshirt up over one's head.
causes for a hood up day may include: flu, swine flu, man flu, female "tummy aches", TVOD, GFDI
(girlfriend disengagement illness), BFDI
(boyfriend disengagement illness), embarassment, lazyness, depression, cock blocking
, WBCFS (work backlog chronic fatigue syndrome), FPS withdrawal syndrome, being mauled by a bear, failing an exam, rape, car sickness, realisation of lack of funds, watching "marley and me", bad night's sleep, no night's sleep, post mid day nap dizziness, dehydration, hunger, bad hair day, failure (all forms) and rejection
However the most common cause of a hood up day is the consumption of copious ammounts of alcohol the previous night, resulting in a catostrophic hangover.