The Leath Hedger, also known as the reverse joker, or the smiling skull, is
the surgical scar left after a hair
transplant procedure known as a follicular unit extraction (
FUE).
Timmy can never shave his head again because of the Leath Hedger
scar at the back of his head. He looks like
the joker from the new
batman movie put a "smile on the back of his head"