For people who read the Light Novels.
* Drink one whenever Issei does something perverted, especially if he mentions anything about breasts ('''WARNING: YOU WILL NOT MAKE IT TO THE END OF VOLUME 1'''). Drink twice if it's not him.
* Drink one whenever Issei gets a shiny new power up thanks to Rias' breasts.
* Drink one whenever Irina's wings flicker from angel to fallen angel.
* Drink one whenever the church trio (Asia, Xenovia, and Irina) pray to God. Take another shot if either of the first two get a headache as a result.
* Drink one whenever Akeno teases Issei.
* Drink one whenever Issei makes a FirstPersonSmartass comment. Drink twice if it's [[SwitchingPOV Kiba or Azazel.]] [[spoiler: [[UnexpectedCharacter Or Fenrir.]]]]
* Drink one whenever anyone [[MomentKiller kills a moment.]] Drink twice if it's Ophis.
* Drink one whenever Koneko [[LittleMissSnarker makes a snarky comment.]]
* Drink one whenever [[HeroicSelfDeprecation Issei starts ranting about how much of a loser he is.]] Drink twice if [[YouAreBetterThanYouThinkYouAre at least one of his haremettes tries to comfort him.]]
* Drink one whenever Issei gets either MarshmallowHell or a LapPillow by the ladies.
* Down one bottle whenever either [[ButtMonkey Ddraig or Albion]] get into another one of their HeroicBSOD moments.