The 'Bachelor' and "Bachelor in Paradise" fan favorite hit up Laguna Beach Sunday with BF, Bobby Jacobs ... showing plenty of PDA. It's the first time we've seen them out together since Amanda's arrest last week in Vegas after a drunken post-bachelorette party incident with Bobby.

As we first reported ... security at the Encore was responding to a noise complaint when an apparently boozed-up Amanda tried to intervene, shoving Bobby in the process. We're told that was enough for security to call cops, who arrested Amanda for misdemeanor domestic battery.

According to the police report, obtained by TMZ, Bobby also claims Amanda started to hit him while he was in bed, argued for hours and at one point took the room's phone and swung it at him. Bobby also says Amanda tried kicking him and he tried pinning her down but he says she kept scratching and pinching his arms and body. Amanda had apparently been upset with Bobby 'cause he wasn't answering her calls.

A rep for Amanda told us it was all a misunderstanding ... calling the shove "playful."