A fake or a copy of someone or something. Chinatown has some of the best knock-off bags, shades, etc. Chinatown is considered Lil China located in Manhattan. The word knock-off basically means fake. So put two and two together. A Chinatown Knock-off is something or someone who's fake.
Bob: Im at the top at the spectrum and you're at the bottom.
Tom: Yea ok....
Bob: You try your hardest to be like me. You're nothing but a Chinatown Knock-off compared to me.
Tom: Look man, you can call me whatever you want to but remember, everything legit that I get you always happen to get the non authentic version and try to be upscale.
Tom: Yea oooooh is right.