Green’s Dictionary of Slang

ABC n.2

[abbr.]

1. (Aus.) Australian-born Chinese; also as adj.

A. Hick Chinese in Aus. n.p.: She described herself with slightly sardonic amusement as an ABC.
Hotblack’s Hot Page [Internet] Odes Poon is an ABC, an Australian-Born Chinese, which basically meant that he said things like ‘G’day’ and called people ‘mate’ while looking like a chubby Bruce Lee.
timeout.com (Sydney) [Internet] Kylie Kwong is an ABC (Australian-born Chinese) cook who listened very carefully to her grandmother and mother, then took what she’d learnt at home to a professional kitchen.

2. (US) American-born Chinese; also as adj.

Walton & Jones Detective Agency 143: The man snidely remarks, ‘you smart for ABC girl.’ Lydia [...] rejects the designation ‘girl’: ‘ABC, that’s American-Born Chinese. Girl, that’s not me’.

3. see American business college under American adj.