A nick name for any of your Irish friends that have a "Mc" in the front on their name that are always mooching. Bumming cigarettes, beers, food, clothes and just about anything they can mooch. They will most often "forget" their wallet when eating out and have to borrow though never to pay back. They can however be very generous when money is available to them and blow through it immediately which is why they never have anything.
McMooch, I can't believe you forgot your wallet again and need to hold 10.