A lesson they will remember.
Urban Dictionary defines mullet ratio as a mathematical term used to describe how extreme a mullet hairstyle is. It is found by comparing how long the hair on to of the head is compared to how long the hair hangs at the back of the neck.
The best way to see the lesson is read Mr. V's class here: http://mrvaudrey.wordpress.com/2012/05/03/the-only-lesson-theyll-remember/
So if you read the above link and found your way back here, there is one more thing I would add to the lesson and it would be to sort the pictures on a graph and it would be a graph with ratios compared to good ones, high ratios would be on one side, low ratios on the other. It should come out to the better looking mullets have a close ratio and the outliers have worse mullets than any other.
A good extension activity would be to request iPads and have students find mullets: good ones, bad ones, and the truly awful ones. Calculate and have the students have their own poster boards in groups and present their findings to the class.