"You canker blossom!" 3 Shakespearean Insults
1824, "the policy of opposition;" see negative + -ism. In a psychological sense, it is attested from 1892.
negativism neg·a·tiv·ism (něg'ə-tĭ-vĭz'əm)n. A tendency to do the opposite of what one is requested to do, or to resist stubbornly for no apparent reason.