Green’s Dictionary of Slang

(US Und.) a stupid person.

1926		J. Black You Can’t Win (2000) 111: When a bums’ ‘convention’ is to be held, the jungle is first cleared of all outsiders such as ‘gay cats,’ ‘dingbats,’ ‘whangs,’ ‘bindle stiffs’, ‘jungle buzzards’, and ‘scissors bills.’.
1935		A.J. Pollock Und. Speaks n.p.: Whang, an ignorant, loud mouthed person.