Drink one sip if any of the 5 main characters are drinking in a scene (the rule resets when the scene changes).
Then drink once anytime:

Show Specific

Someone says Racist
Someone gives a bad comeback "Well, you're dumb!"
Sniffing glue is referenced or actually attempted
Someone talks about popping off a shirt
Someone says Bang
Someone says Boom or Bam
Someone says Hey-Oh
Someone says talent
Someone pulls out a gun they were hiding

Character Specific

They mention Charlie Work
Charlie gets flustered
Charlie's illiteracy is referenced
Dee stands up for whats right
Dee's backbrace or Scoliosis is referenced
Mac says Bitch
Mac tries to assert himself as a leader
Rob McElehenny is shown in beginning credits
Dennis feels insecure
Frank mentions gambling
Frank says Whore