Remember when Nick Jonas was the littlest Jonas brother? Not hyper-coiffed Joe or the awkward Kevin — but the baby-faced youngest brother of the Disney-bred, promise ring-wearing band that gave us such hits as “Lovebug” and “Wedding Bells.” Well, he’s an adult now, with a successful solo career, a collection of bomber jackets that won’t quit and a relatively disgraceful grasp on the electric guitar. The video for his latest “Chainsaw” dropped today and features lyrics (with matching imagery!) such as, “I took a chainsaw to the sofa where I held your body for so long.” Concerning? Maybe. But it’s damn catchy.