"If a student tries to use me then I shall use them back unmercifully." (John Kells)

This is, actually, unavoidable, because the last thing the master is prepared to do is waste either time or energy. And this statement shows how great teachers always speak in principle. Even at their most personal and idiosyncratic (psychotic), their utterances easily generalize up and into each person present. Any form of abuse or misuse will eventually backfire.