It is when you give a mullet to your dick.
I walked into the bathroom today and my boy Rob was shaving himself a dillet.
A noun used to refer to any one of several extremely sensitive parts of the body. Typically a part of the body most suceptible to shackdackling.
"Dooood, did you shackdackle your dillet?"
Response: "Nah, I ska-danked it."