The common connotation is of a person who speaks Chinese with an American accent, English with a Asian accent, and can't use chopsticks properly.
Most likely forced to pick up the piano or violin at a young age and/or sent to Chinese school. Often pressured to attain perfect SAT scores or straight A's in school.
ABC: Um...er....Ni how ma? ^^;;
Chinese person: Aya~ You are ABC.