but wot did ZXCVB say? aik to yahan lath maar editing hoti hai... saray ka sara hi edit kar diya
here is my take on the issue...
the reason it is considered a gali is because men in the subcontinent are very protective and sensitive about their sisters and don't tolerate discussion of or a reference to their sisters amongst other guys. when someone calls someone else a sala, they are implying they are/will be married to that person's sister, when in actuality they are not. Hence it is considered a gali.
yaar thank you for putting it in a more readable format that the blunt response ZXCVB had written :D
sorry for editing that out, you must have felt left out:-p