Not a socially acceptable word, used by very ignorant people who are not very intelligent.
During the 1950's & 60's people would actualy chase Abiriginals off their propery with 4wd's, & it's reported that 'boong' is the sound they make when they hit the bull bar.
"blake has a boong nose"
"fuck off you boong"
"no you cant have a dollar you boong"
"im not going there, too many boongs"
"id rather keep my shoes you fucking boong"