Literally translated, means 'red-head's shit' or 'Caucasian shit'. Used to describe Asians or Chinese who are unable to speak any of the Chinese Language dialects (their native languages or mother tongue), but who are able to speak English. Not necessarily a derogatory or rude term, but originated as such to mock the Chinese who would/could only speak English.
That stupid little ang moh sai thinks she's too good for us!
Aiyah, why waste your time trying to teach that ang moh sai.