This is an acronym for "Onion My God".
Amelia texted "Ong". Anna asked, "What is ong?". Anna rolled her eyes, "it stands for onion my god," she sighs terribly.
Ong is a way of saying “on god” or for christians using the lords name in vain.
“I hate that girl like ugh”
“Ong she’s so annoying”
It is short for On God, to express support for a notion/subject.
" Her fit ain't it" then one will reply with "Ong!"