Mary Hart isn’t stepping down too gracefully from her “Entertainment Tonight” anchor seat that she’s held for 29 years, some say. Lara Spencer, a rising star from “The Insider” who’s vying for Hart’s job, recently misspoke on a red carpet, calling herself the host of “Entertainment Tonight.” A source says Hart, who rarely leaves the studio for a red carpet, flipped out when she saw the footage on the monitor. “She competely lost it and tossed her coffee at the screen,” our insider says. Hart later allegedly apologized. Reps from “ET” said the outburst never happened.