Barnes -- who's now a free agent -- was hangin' at the beach last night when he told us, "Manhattan Beach doesn't like me very much ... I don't know why they don't like me, but they don't like me."

Barnes was referencing an incident on July 30 ... when he was arrested on an outstanding traffic warrant. We're told the arresting officer lurked near Matt's car for two hours on the night of the arrest to make sure he didn't miss the chance to arrest Barnes.

When asked if he thought he was being watched that night, Matt told us, "Someone waits outside your car for two hours ... I would say that's watching."

Barnes explained that his beef isn't with the entire Manhattan Beach PD ... saying he "loves" the cops ... and insists. "We're not gonna let a couple of situations take us away from living our lives."