Monty Python and the Holy Grail

Instructions on how to use the Holy Hand Grenade of Antioch
  1. And the Lord spake, saying, First shalt thou take out the Holy Pin.
  2. Then, shalt thou count to three, no more, no less.
  3. Three shalt be the number thou shalt count, and the number of the counting shalt be three.
  4. Four shalt thou not count, nor either count thou two, excepting that thou then proceed to three.
  5. Five is right out.
  6. Once the number three, being the third number, be reached, then lobbest thou thy Holy Hand Grenade of Antioch towards thy foe, who being naughty in my sight, shall snuf it.
Please! This is supposed to be a happy occasion. Let’s not bicker and argue over who killed who.
— 

King of Swamp Castle, Monty Python and the Holy Grail (1975)

Also applicable to any family gathering on Once Upon a Time