A rumor that gets spread so fast that everyone knows it in at least 30 seconds.
Lets say that you never got a girlfriend in your life and you tell your friends at school at work. Since you told them its your first girlfriend they start to spread it and becomes a uncontrollable wildfire.
Don't tell anyone about this. It will spread like wildfire!
The act of setting a girl who is currently PMSing's tampon string on fire and then letting it set her bush on fire. As a bonus you can put out the fire with your semen or piss.