Serbian, Croatian, Slovenian racial slur. It comes from the fact that these countries were part of the former Yugoslavia. It can be offensive because of the bad Yugoslav wars.
What an Indian store owner calls a white,pot smoking,curly haired employee,who never shows up on time or at all,and does no work what so ever even when he does show up,and leaves early.
An expression used in the card game "Texas Hold 'em Poker" for someone who was losing the hand to one or more players, and was saved by the 5th card, the river, due only to luck, and won the hand.
Bob: "All in"
Stew: "... I call"
Bob: "haha, I'm beating you with the odds of 4:1 in favour of me, you only have 3 cards you can hit out of the deck, with one card left, what a crappy call and a horrible read"
Stew: *hits the '3' he needed on the river card*
Bob: "OH MY GOD, HOW LUCKY CAN YOU GET? GO PLAY SLOT MACHINES YOU RIVER NIGGER!"
It refers originally to slavery times, when black women used to be raped by the white slave owners to produce mixed children. They would usually grow up working in the plantation house and sometimes would receive education, unlike the black slaves who worked outside in the fields.
The mixed children would associate with whites and have privileges the slaves did not.
Now the term refers in a derogatory manner to lighter-skinned people of color, who are sometimes perceived as acting superior to darker-skinned people, and who because of their color, association with whites in what is viewed as a fawning manner, and greater success in life are sometimes resented by those less fortunate.
Since Rasheed got that office job, he is full of himself and acting like a house nigger.