How can I make my message stick?

The police have issued this warning: "If you are driving after dark and see an oncoming car with no headlights on, DO NOT FLASH YOUR LIGHTS AT THEM!" Why? Because the no-headlights car is being driven by a gang member, and as part of an initiation rite, the first person who flashes him will be hunted down and killed.

We have all heard this urban legend, but more importantly we can all remember it. But why?
Why do messages like this and others STICK?

[REST]
1. Remarkable:
Make something worth talking about. As you drive down the motorway you see cows in the fields. Nobody rushes home to tell their friends they saw a cow on t

2. Emotional:
Make the message trigger the emotions. The more intense the emotion, the more likely individuals are to talk about it. Fear, Happiness, Laughter, Joy.. all spices work equally well.

3. Public Service:
When someone shares this legend with you, they feel like they're doing a public service. They might believe they're saving your life. And that's the second trait of viral ideas. It's often a small favour.

4. Trigger:
A trigger is an environmental reminder to talk about an idea. For instance, a golf tournament is an excuse to trot out your public-service info about the state of Tiger's knee, and a cup of coffee reminds you to talk about Starbucks's no-decaf-after-noon policy. A glass excuse is a trigger to talk about the purple cow, in case you didn't need one.