On Mar. 17, St, Patrick's Day revelers from all over the world will gussy up in green and descend on Manhattan for the world's oldest and largest parade of its kind, drawing approximately 150,000 marchers, around 2 million spectators, and nearly as many bagpipes. For the army of bartenders working the front lines this coming Tuesday, the annual scrum is the ultimate test of a malt-pourer’s mettle — think “Braveheart” meets “Cocktail.”