Idiot. ‘Galah’ is often used as a reproach by avuncular male soap-opera characters to demonstrate their superior old-timey Aussieness. Expressions such as ‘flamin galah’ and ‘stone the crows’ constitute the language of a post-sex life.
Example of ‘Galah’
Jessie, you flamin’ galah! Why would you do a stupid thing like putting petrol in my diesel engine? Now get back to your cushy part-time job in the local cafe/surf shop.