i did not get the joke

i suppose that the cop was saying a bunch of racist things about chinese people a couple of seconds earlier when he was in the cop car
and then when he comes back after shooting her he claims that he shot her cause she called him a N word (can you write that word on imdb by the way?)

and then later he blaims the postal dude for the murder of her, claiming that she was a poor innocent sweet woman

Hey Mike. I suppose, if you are american, you know the common prejudice in America about asian people being the worst drivers. I guess "Drawn Together" even had an episode about it.

Anyhow, the colored cop makes some remarks about immigrants, walks up to her, kills her and then has this made up excuse about her coming up with some racist remarks. The joke is basically the bigotry coming from him as a minority that had and has to deal with prejudices but killing her for the same reason while abusing his power as a law enforcment officer in the nastiest way possible.

Mind you, of course the violence is totally overblown, but that's just true to the game it's based on and runs with the film.