Did you hear the one about the drunk in the jail cell? Dennis Vargas hasn’t written this joke yet, but he has the perfect chops to do so. He’s a full-time jailer for the Garden Grove PD by day and a stand-up comedian by night, most recently performing at the Improv in Ontario. While throwing perps in the slammer and tossing out arresting one-liners may not seem like a natural combo, for Vargas, 40, the duel pursuits are a perfect fit. “If you have a high-stress job, you need an outlet,” says Vargas, who since 2003 has managed the Garden…