In between talking about himself and dating celebrities with “Wonderland” bodies, tabloid fixture John Mayer sings blue-eyed soft-rock and plays the guitar. Expect lots of bantermuch of it self-aggrandizing, some of it defensively sowhen Mayer headlines a 7:30 p.m. Marcus Amphitheater show tonight with fellow singer-songwriters Colbie Caillat and Brett Dennen.
