A popular word used by people with colorful and inside humor. "McFucking" does not have anything to do with McDonald's, It's simply a cute way of saying "fucking".
Making an absurd amount of money, usually by crooked means. Making money to the point that if you were to liquidate your funds, you could swim in your money, insofar as that's possible, like Scrooge McDuck.
Big oil executives were seriously Scrooge McDuckin' last quater. They maderecord profits by price gouging.