Sean Penn Loud and Proud at Polo Lounge

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Sean Penn tried to be super stealthy when he interviewed El Chapo, but he was a loud bragger in the middle of a restaurant just before the story broke ... according to Page Six.

Sean was reportedly holding court during Golden Globes weekend at the famed Polo Lounge, a watering hole for celebs. Page Six says Penn was strategizing with his crew which included a former State Dept. employee. One spy said, "He was running around like Woodward and Bernstein at the Washington Post ... they were loudly talking about El Chapo."

0112-polo-lounge-facebookThe spy says Penn and company were concerned that Mexican actress Kate del Castillo "was going to write her side of the story ... [Penn] was like, 'She wants to be on Charlie Rose instead of me!'"

Page Six got a "no comment" from Penn's rep.