Every time they go "uh": One drink.
Any word or phrase that's repeated three or more times: One drink per occurrence from the third time on.
Any background noise that blots out the audio: Drink as long as it persists. WARNING BE CAREFUL WITH THIS ONE!
Reviewer either starts mumbling inaudibly or moves far enough from the mic that you can't hear them: Drink until you can understand them again. WARNING BE CAREFUL WITH THIS ONE!
Reviewer treats you to the sounds of their asthma/emphysema: Whole drink.
Reads the instructions for what they're reviewing: Whole drink.
Camera is aimed at a still life of what's being reviewed for entire video: Whole drink.
Reviewer coon-fingers part in the still life while rambling: Drink as long as it persists. WARNING BE CAREFUL WITH THIS ONE!
Add your favorites in the comments.