When you're trying to figure out whether doing something is a good idea or not, there are various rules that come in to play, such as Have Fun, Do No Harm, Have Fun (again), What Happens in Vegas, etc.

Rule Zero, the rule that always comes before all the others, the most important, basic rule of doing anything is: "Don't be on fire."
- I can't get this bbq to light.
- Here, use some petrol.
- I am not breaking Rule Zero to cook a burger.

- Hey, let's see what happens if I fill my foreskin with lighter fluid and light it.
- I am invoking Rule... wait... yeah, go ahead, that'll be funny.
by tbrd June 15, 2010
The customer said this happened. Dude...Remember Rule Zero!
by Tech Support Rep January 18, 2012
A rule on the internet which stands for don’t fuck with cats
Luka Magnotta broke rule zero when he killed 2 kittens.
by VSCOboy3000 December 20, 2019
Garry: Hey! look at this stupid cat lol!
You (most likely):Internet rule zero, RULE ZER-OH
by Internet Rules 101 July 29, 2022