The act of having a messy masturbating session whilst taking a dump at the same time. Added to this is the fact that when you come to clean up time and your quite aggrieved by the amount of mess you have made you will usually find yourself utter the phrase "Good Grief"
Last night I had a Charlie Brown wank as I found myself saying Good Grief at the mess I made.
Basically this is the ratio applied to foodstuffs, by fat people whereby whatever the packaging states as how many people the foodstuff serves is divided by a minimum of 2. Used frequently in the North of England......
Fatlady: Says 'ere this cheesecake serves 4 people.
Fatlad: Well using Fatlad's Food Ratio, as we are fat, thats 2 people in our case!