Take a drink every time someone says "OHHHHHH!" or any variant thereof.
Take another drink if it's not Mordecai or Rigby that says it.
Take a drink every time someone says "Dude."
Take a drink every time Muscle Man says "My Mom!"
Take a drink every time Benson yells at someone.
Take another drink if he turns red in the process.
Take a drink if he manages to turn red without yelling in the process.
Take a drink every time Benson threatens to fire someone.
Two drinks if it's Mordecai and/or Rigby.
Three drinks if he actually fires someone. Four if it's not Mordecai and/or Rigby
A special case: Down your entire glass each time you see the very end of "Best Boss in the World". Why? Because Benson threatens to fire all of his employees. Not just including Muscle Man and High-Five Ghost, but also Skips, Thomas, and even Pops! Remember back in "Think Positive", where he was going to do the same thing to him? Take that in with your drink.
Concluding this, take a drink if a person he fired gets rehired by the end of the episode.
Take a drink every time Rigby screams.
Take another drink if it's something intelligible (Ex: "SHUT UP!" or "STOP TALKING!")
Take a drink every time a reference is made to a person or event from a previous episode.
Take a drink every time you hear Skips say, "I've seen this before."
Take a drink every time Pops offers a lollipop as money.
Take a shot when Pops says, "Good show!", or some variation.
Take a shot for every '70s, '80s or '90s song featured in the show.
Take a shot every time Mordecai punches Rigby for something stupid, Jerkass, or dirty.