A theory based on the fact that sick days should always be spent at school and not at home where they will only be wasted.
The reason being that if you are sick, you should go to school, because not only will you be spreading disease to all those evil bastards you put up with every day, but you won't be counted absent. Also, why stay at home if the only thing you'll be doing is blowing snot into a tissue? The only reason anyone should ever stay home from school is if they plan to do something worthwhile, like experimenting with liquor or weed.
Some say "Well, when I'm sick all I feel like doing is sleeping." Sleep at school. Once you find the perfect position, those desks aren't nearly as uncomfortable.
"Brigand" is the french word for "bandit." It's deemed the Brigand Theory because you're stealing the health of all your classmates and teachers.
dude 1: Dude, you are so freakin' sick. Why are you going to school?
dude 2: I figure I'll put the Brigand Theory to good use and puke in Pre-Cal.