“Fat Actress” Kirstie Alley, tripping the light fantastic with her pooches at an LA park, recoiled in horror when several 20-ish guys started cat-calling stuff like: “Hey, you’re the chick from ‘Cheers’ . . . Man, you really packed on the pounds since then!” Kirstie turned beet-red, trying to ignore the creeps as she packed her dogs into her SUV, but the bullying mouth-breathers kept hurling “fat” cracks — until a muscular dude walked up to them and growled: “You boys have a problem?” Slack-jawed, the punks shrank back as action-hero Vin Diesel stepped up in their faces. “I think you boys owe this lady an apology,” he said evenly. The wanna-be tough guys instantly wimped, apologized to Kirstie, and split. Holding back tears, Kirstie thanked Diesel profusely for his fast and furious gallantry.