Huh?

Saale!! Hum tumhari maa behen ek kar denge!!
(rough translation : Asshole! I/We will make your mother and sister One!)

Huh?

I mean, what IS that? It doesn't even make sense, leave alone being insulting. I've heard my friends, more often than not from the northern parts of the country, scream this at the guys we were warning or fighting with. And I always wondered, just because you said maa AND behen in the same sentence, it becomes an insult? How can you make someone's mother and sister 'one'? I used to have to stop myself from laughing whenever I heard this.

Any northies reading this - care to explain?