It just makes him mad:
Police said that 6-foot-4 street performer was seen arguing with a 32-year-old Star Line Tours tour guide, who had expressed concern that the wookie impersonator was "harassing and touching tourists" in violation of the city law.
... The Star Line Tours guide, Brian Sapir, said in an interview today that the Chewbacca character was harassing two young Japanese tourists when he told him to stop. "You could see him exploding in his mask," Sapir said. "He said, 'Nobody tells this wookie what to do."
Young then threw his mask off and head-butted him, Sapir added.