John Mayer's got Shia LaBeouf's back these days it seems. The singer went on a Twitter spree Wednesday morning defending the actor's latest controversial (and wacky) behavior. "Re: Shia. Being young and very talented/successful is like dropping in to the top of Mount Everest via helicopter," Mayer wrote. "There are moments in life where you need to feel quantum shift, movement. And if where you already are is considered the top…" He added, "The dumb people disintegrate, and the…