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1.
A McRumor is simply that. A rumor started by McDonald's restaurant employees about other employees, generally usually widespread like a plague due to the staggering of shifts. It may be up to a week before a McDonald's employee hears of such rumor about themselves, at which time, they are normally the last ones to know and must face ridicule by their fellow employees.

In most cases. These Rumors are false. And started by someone with a vendetta.
Employee one: "OMG did you hear that Bill slept with Jean?"
Employee two: "No way he also slept with Synthia and Jackie!"

Employee one: "He's such a McWhore"

Employee one: "Did you hear the new McRumor going around?"
Employee two: "About Bill?"
Employee one: "No! about Synthia getting transferred because managers aren't supposed to sleep with crew!"
by McSlave01 January 18, 2012