Originates from Maynard James Keenan of Tool; but also from the conversion: of 'Man' to 'Mayne' to 'Maynard'
Usually only used between close confidants.
As a farewell:
Person 2: "F*ck off maynard."
Originates from the word manatee (manati) which has evolved over time to become "maynard"
"Omg what a maynard"