According to his handful of readers, budding novelist Mosley Forstner, 23, thinks that people shrug with much greater frequency than they actually do. 'Every time a character responds to something in Mosley's book, it's ''Suppose that's the way of things,' she shrugged' or ''Fine, then I'm leaving,' he shrugged,'' said Rodney Klein, a fellow student and peer reviewer of Forstner's. 'Can't his characters just 'say' something once in a while?' When informed of the criticism, Forstner responded with a grunt and a curt, dismissive motion of his shoulders intended to convey nonchalance. 