A dope, fool, idiot, or nincompoop.
Unbelievably stupid person.
Might have been derived from moron: adding an extra letter "o" to moron meaning double-moron, thus a maroon.
Usually preceded by the words "what a"...
vanilla with chocolate syrup--what a maroon!
He thought that wax fruit was real--what a maroon!
He fell in love with a stripper again--what a maroon!
Second Person: Na no way mate, this is year of the mighty MAROONS