We are made of starstuff.
When a Player Drinks
When you have Disadvantage and roll a 1
Drinks a potion
Drinks alcohol in character
Is hit by a trap
Every time your alignment gets in the way of your plan
When the DM Drinks
When a player has Advantage and rolls a 20
A Character Finds a Magic Item
A Character Disables a Trap
An NPC Drinks (in character)
An NPC is humiliated
A Geek Media Reference is Made (Leroy Jenkins, Monty Python, Attacking the Darkness, etc)
The offending party takes 2 drinks any damn time batman is referenced or a batman voice is used.