Finish your drink and Head Desk if an ally is AFK for the entire match. Feel free to drink some more if he reconnects much later and dies over and over trying to engage level 12+ enemies when he's level one.
Take a shot every time you accidentally Kill Steal.
Take another if you're a support or tank and a carry really needed it.
Take two if the person yells at you for it and doesn't believe it was accidental.
Take a drink and Face Palm when someone on your time tries to imitate a famous player's crazy playstyle or unconventional build and fails miserably at it.
Take a shot whenever you try to help a team mate get a jungle buff and end up stealing it instead.
Chug your drink whenever your champion is channelling an ability for more than one second. If you're feeling hardcore, do this for recall as well.
Take a drink every time a tower goes down,
And two for an inhibitor.
Take two drinks if your team takes Dragon,
And finish your glass for Baron Nashor.
Finish two glasses should you steal Dragon with a blind skillshot. Finish three should you do so on Baron Nashor.
The same as summoner's rift, but:
Replace Baron Nashor with Vilemaw.
Take another two drinks for a triple kill.
Drink every time you control both altars.
Take a celebratory shot every time you manage to control all 5 points.
Conversely take a shot of shame if the enemy controls all of them simultaneously.
Chug while you are capturing.
Take a drink and snicker to yourself every time you cap a point by yourself completely uncontested (likely through sneaking behind enemy lines and ninja-ing an unguarded point).
Take a shot when a lane demands to be ganked with unwarranted rudeness. Take two if you actually do help them out and they don't go in with you. Take an extra shot for every time you ping indicating you're about to gank.
As Alistar, take a drink of shame every time you knock back an enemy with Headbutt in a position that is actually favorable for them. Take a drink of triumph for every Headbutt canceled into Pulverize that you pull off.
As Pantheon, chug triumphantly should you manage to damage at least one enemy champion with Grand Skyfall. Chug twice should you kill at least one enemy this way!
As Janna, take a drink of shame every time your Monsoon doesn't work as you hoped. Do this as well if you continue to channel Monsoon and get yourself killed for it.
As Blitzcrank, finish your glass for every time you pulled an enemy champion from the fog of war with Rocket Grab.
Down a shot if you accidentally kill your opponent with your Rocket Grab. Two if someone calls you out on it.
As Nidalee, finish your glass for every Javelin Toss you throw into the fog of war that ends up killing an enemy champion.
As Sona, take a shot for every Power Chord you apply onto a champion. Take a sip instead if you don't feel like having your stomach pumped afterwards.
As Ryze, take a sip for every time your passive makes Overload immediately available to you again (pretty likely to kill you if the match lasts at least 30 minutes).
As Cassiopeia, take a sip for every time Twin Fang gets its cooldown refreshed from hitting a poisoned champion (pretty likely to kill you if you can somehow still aim enough to poison champions while drunk).
As Skarner, please do not take a sip every time you use Crystal Slash. It will definitely kill you.
Or doing this as Karthus every time you use Lay Waste.
Making use of a drinking hat!... which apparently is attached to a few kegs.
As Swain, drown your sorrows if your Mana Meterruns out at the most inconvenient moment and everyone gangs up on and kills your defenseless human form. Also applies to Anivia if you were counting on Glacial Storm acting as a no-man's-land between your and their team and you all get jumped the moment it stops casting.