Bartenders, be warned, Robert De Niro is very particular about his cocktails. He recently instructed waiters at Swifty’s and at Lucky Strike Lanes how to make a “halftini” — and it makes James Bond’s “shaken, not stirred” mantra seem like minor mixology. At Swifty’s, our spies report, the drill was: Fill a shaker with ice to the top; squeeze in five lemon twists; use Absolut vodka and “a little extra” dry vermouth. Shake very well until ice cold. (Adds a Lucky Strike witness: “Very well” means, “until the bartender couldn’t shake the glass anymore.”) Strain the drink twice into a cold martini glass with three more twists. Serve.