Do the math.

Customer: "What size McNuggets do you have"?

Cashier: "We have 6, 9, and 12 piece McNuggets".

Customer: "I'll take the half dozen".

Cashier: "We don't have that size. Only 6, 9, and 12 pieces".

Are they named after this fella?

"I went down to Mickey D's and got me some Chicken McDouglas."