A man with an absurd amount or smegma (dick cheese) which is used to make 3D models of Sharks. It is commonly used as an insult towards the uncircumcised smegma havers.
Person 1: "Damn bro, I have a lot of smegma."
Person 2: "You should become a Smegmadon"
Smegadon is the build up of smegma on a manspenis in jurassic proportions.
Girl: Tonight is your luck night big boy.
Boy: (pulls down pants)
Girl: I no longer wish to give you a blow job as it seems you have a large Smegadon residing on the end of your penis.