Zachary Taylor was easily one of the most disheveled-looking American presidents. Just look at one of his more famous mug shots. It's day three of one of his epic whiskey benders somewhere on the frontier, which might be close to the truth because he died only 16 months into his term. His official cause of death is "bilious diarrhea," so perhaps we should cut him some slack.
Some interesting side-notes:
Piece six in OrangeCoat's month long celebration of the bald and bearded presidents of the United States.