You could get quite drunk if you took a drink for every Gibbs Slap, McGee gets a new name from DiNozzo, a main character is in immediate danger, or if you see a gun (which is not always the same as the immediate danger).
Concerning the Gibbs Slap: drink twice for every one that's not borne of annoyance, or that's actually plot-relevant.note Such as the time when Ziva used Gibbs' hand to Gibbs Slap herself as a way to restore his memory. Drink a whole bottle when Gibbs either has someone do it to him, or he does it to himself.
Drain your glass whenever someone other than Gibbs slaps Tony.
Take a shot whenever Abby gets given a Caf-Pow, she talks about a piece of lab equipment as if it was a person, and two when you see her back tattoos.
Or when Gibbs thanks her for her good work by kissing her cheek/forehead, and two if he also gives her a Caf-Pow.
Take two whenever she runs up to Gibbs while shouting "Gibbs! Gibbs! Gibbs!" Genki Girl-style.
Take a shot or two if the show opens with somebody stumbling on a dead body (in a humorous sort of way), followed by random chatter in the squadroom that sets up that episode's comedic subplot(s).
Take a shot every time a guest star is attractive, and/or has UST with a main character, and/or the main characters Love Interest is jealous.
Take a shot every time Ziva teases DiNozzo in a highly suggestive manner, McGee's technical explanation is interrupted by someone, and when Ducky's mother appears or is mentioned. Drink when someone asks how he gets the boat out of the basement. (For those not using alcohol, drink when Ducky says "This reminds me of...", don't do this if you use proper drinks.)
During one of the marathons that they tend to run on USA Network, take one every time Ziva messes up a piece of American slang.
Better yet: take one every time Ziva doesn't understand some form of Western culture. Or when Gibbs is tech-illiterate.
On the DVD commentary for "Twilight," Michael Weatherly, Pauley Perrette, and John C. Kelley direct the audience to "take a drink of your favorite beverage every time someone dies or almost dies."
Take a shot every time Gibbs gets impatient with any long-winded chatter from Ducky or Abby.
Take a shot every time a movie reference is made. Take two if the character making the reference is not Tony. Drain your glass if the reference turns out to be genuinely helpful in solving the case.