Top definition
The unique combination of a McDonald's double cheesburger and a single chicken McNugget which is placed on top of the kangaroo (hamburger) patties
McDonald's Staff: "Can I take your order?"
Mercer: "Lemme get two McFoos to go"
McDonald's Staff: "What the hell is a McFoo?"
Mercer: "Put a chicken nugget on top of that double cheeseburger for me playa!"

by devreser March 03, 2007
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