To understand what exactly a mullet is you have to read this!
mullet* (mu' lit) 1. any of a family of edible, spiny-rayed fishes found in fresh and salt waters and having a small mouth and feeble teeth, as the striped (or gray) mullet. 2. any haircut which the sides and top of the hair are significantly shorter than the back.
The origin of the term "mullet" has been traced back to the film "Cool Hand Luke." One of the guys calls people with long, shaggy hair "Mulletheads." A legend is born.