A lip-syncing low
I admire Steve McQueen's subtle acting talent,but his abilities obviously didn't include playing a rock 'n' roll star. His couple of scenes fronting a local band are laughable. His mugging and lip-syncing are so exaggerated, it's painful to watch.
Side note: Check out the guitarist in McQueen's band. Bless my soul, it appears to be none other than Glen Campbell, who was probably doing studio work with the Beach Boys about that time, too.