In 1977, while AC/DC were supporting Black Sabbath on a European tour, Geezer Butler and Malcolm Young were involved in a tense hotel-bar confrontation. Young later said Butler, who had been drinking, produced a flick knife after Young dismissed his complaints about Black Sabbath’s long career; Ozzy Osbourne reportedly intervened and told Butler to go to bed. The incident became part of the tour’s lore and reportedly contributed to AC/DC being removed from the bill.

Butler later disputed that he had pulled the knife on Young, saying he had bought it in Switzerland and was merely flicking it while arguing with the guitarist. He said Young had criticised Black Sabbath and challenged him over carrying the knife, but insisted nobody was harmed. Other accounts describe the object as a toy flick-knife comb, leaving the exact nature of the incident contested.