For those who gotta feel it to believe it!

RULES ARE IN BETA: If you have any suggestions add me (King). I want to make this the easiest and widest spread l4d drinking game there is. TRY TO KEEP THE RULES WE HAVE OPEN IN STEAM SO YOU CAN SHIFT-TAB TO CHECK THEM AS INFECTED. THIS WILL HELP REMEMBER AND MEMORIZE.

There are several drinking games that can apply to l4d/2. First, choose the drinking game that fits your team's needs. Warp the rules for your own playstyle! Devise your own numbers of drinks! Discuss in group comments!

HUNTERS:
Survivors: Drink for every ding of damage while you're pounced
Infected: Drink for every ding of damage you deal to the survivor. BE READY TO SET IT DOWN!
[best for l4d1... can also be applied to all infected for l4d2, though the game is still called 'hunters'.]

HEALTH:
Survivors: Drink at the end of the round for every time you had to heal or take pills (or adrenaline L4d2 only)
Infected: Drink if a survivor heals after they hit you!

CLUTCH:
Survivors: Give out a drink to a player in the game (who's playing) for each time you kill an infected without taking damage, or suffering their effects (applies to basically just boomer).
Infected: Give out drinks if you hit a survivor for more than 25 damage. (25 is safe because it's 5 hunter hits or a hit and a slam for charger).

NOOB!:
Survivors: Every time someone fails ("Nice catch!" situation, misses a molo on a tank, runs ahead and gets ♥♥♥♥♥♥, taunts a hunter and gets nailed, etc.) try saying "NOOB!" If you do, and they deserve it, they drink! Drinks should be proportional to their failage.
Infected: Same thing, basically. Nub it up, drink for it.

UMAD!?:
Survivor: Get called "NOOB!" too many times? Know you're bad? Too drunk? Might as well just rage... cuz if you get mad, you may have to drink for it!
Infected: Same.
[EDIT: DO NOT TROLL FOR THESE RULES! LEGITIMACY ONLY! Trolls will be removed from the group.]

Any more ideas for l4d related drinking games are welcome in group chat! Simply say @(playername) and say something positive, I will catch it and throw it on the board. Remember to invite people you know who have a good time drinking and gaming!