"Behnchod" is originally a Hindi word which comes from two separate words: "behn" (meaning: sister) & "chod" (meaning: fucker). So it literally translates into: "sisterfucker", though some people believe it to mean, "child born of her sister". Both the meanings are equally acceptable.
Cultural significance: The most commonly used verbal abuse in India, it has acquired a kind of coolness & cult now, though, many people look down upon those who use it!
Usage: Used normally with the above-implicated meaning most of the times; it is spoken without meaning many a times and acts as a kind of takiya-kallaam (Urdu) for a lot of people i.e. spoken as punctuation in a sentence without the implied meaning. It then, becomes a way of speaking without the desired implication.
In many ways, it can be called the Indian equivalent of the word "fuck", albeit with a sexist overtone.
Get out of my way, behnchod!