The man was offended because Nancy refused to treat him. In order to save face he felt he had to assert himself in front of the other men. Aborigines can't hold their liquor like the white man can. Alcohol brings out the worst in them. This man had always disliked Nancy, but it took some alcohol to give him the courage to tell her what he thought of her.
Aborigines traditionally avoid confrontations unless serious tribal matters are involved.
They don't adhere to this custom when they have consumed too much alcohol. This is the best alternative. Traditionally Aborigines avoided inter-personal confrontations unless the matter was so important that they were obliged to settle it in a formal fight. Women hit each other over the head with a stick and the men speared each other in the legs. This still happens occasionally, but only when serious taboos are broken, e.g. sex offenses or breaches of sacred customs.