Credit: Jean Baptiste Lacroix/

Lindsay Lohan certainly sounded contrite in her confessional Sept. 17 Tweet, in which she admitted to failing a drug test. ("I'm taking responsibility for my actions and am prepared to face the consequences," Lohan, 24, wrote.)

But a witness saw the star craft her statement that night on her Blackberry at Hollywood eatery Magnolia -- and tells the new Us Weekly that a flippant Lohan laughed and quaffed Jack and Cokes as she typed.

Lohan composed her missive as her assistant and a male pal coached her on how to make it "more personal," the witness recounts. "Her friend would say, 'No, use 'setback,' don't say 'mistake.' They'll say you make mistakes all the time!" The friend went on, "It's better to say you're responsible. Denying it will just get everyone mad per usual." Lohan's response: "She giggled" and had her assistant order her another Jack and Coke, the Magnolia spy tells Us.

Once the final copy was sent off to her management team -- Lou Taylor and Larry Rudolph, who famously helped Britney Spears clean up -- Lohan wasn't "emotional," says the witness.

The actress, who has been to rehab four times, even joked about drinking whiskey that night, telling pals, "What are you gonna do? I'm ill" -- making air quotes with her fingers.

Us Weekly also reports that mom Dina told guests at her Sept. 17 birthday party at Madeo's Restaurant in Roslyn Heights, NY, that her daughter - due in court Friday - would get off scot-free. "She said, 'Who cares if it's true? Our new team is like a machine. They'll squash this.'"

To read much more about Lindsay's fake apology, how her closest friends worry "she can't be saved" and how she could be behind bars for longer than she thinks, pick up the new Us Weekly, out now.