It Takes a Gang bang(for me to go down.)

In L4D 1 and 2, We
HUNT THE HUNT OF LIFE- Hunter
BOOM THE BOOM OF LIFE- Boomer
SMOKE THE SMOKE OF LIFE- Smoker
TANK THE TANK OF LIFE- TANK!
SAVE PEOPLE- Survivors

In order to save someone you must brutally murder them, then proceed to kill yourself in some form.