On May 18, Sen. John McCain, the Arizona Republican, began appearing in 2,500 movie theaters around the country. No, it’s not a cameo in Driven, but a 30-second public service ad from the bipartisan Americans for Gun Safety Foundation aimed at moviegoing kids and their parents. (The spot, hitting just as Hollywood unholsters its action-heavy summer movies, is also featured at agsfoundation.com.) How does the former presidential wannabe stack up on the big screen? Hit and miss. His message is stark and straightforward: 40,000 kids bring a gun to school every year, so it’s not snitching if you’re potentially saving your classmates’ lives. But the messenger’s all wrong: Uneasily green-screened on top of a bucolic school setting, the woodenly chummy McCain comes across like Mr. Hand over the PA system. If you’re thinking about packing heat to class, wouldn’t you be more willing to listen to, say, Eminem? And that AGSF logo has got to go: It’s a target, for Pete’s sake. Our grade: B.