snollygoster

snollygoster \SNOL-ee-gos-ter\, noun:

Slang. a clever, unscrupulous person.

A snollygoster is a shyster, and not, as President Truman thought, a man born out of wedlock…
-- Anthony Burgess, Homage to Qwert Yuiop, 1986

"...But you wouldn't be advised, would you, you chuckleheaded old snollygoster!"
-- William Kelley, The Tyree, 1979

This American English slang term, which entered English in the mid-1800s, is of unknown origin.