Most of the time movie scripts are written by people who don't know a community as well as they should. The above seems a case of the writer not being able to understand the basics of the community he/she is writing about and depending only upon stereotypes instead of going out and conducting some research.
I guess most Indian scripts reflect this trend. The script writer goes by popular (or, for that matter a stereotype confined to his immediate friends and community) stereotype and builds the plot and story. In the above script a man is named "Sally" when that is the name usually given to a woman (as in Harry Meets Sally).
Thus the man wearing suspenders and shorts and saying "Kya man, kayko kalipili bomabom karta hai" is a Christian, and a man who wears a sadra (sacred shirt) and says, "Kam karneko mangta hai ni?" is assumed to be a Parsi.
Guess that's the only reason that prevented me from wearing suspenders. The fear of being thus stereotyped. Thus when the whole film is peopled by such characters the effect is one of a feeling of alienation, of the bitter bile rising instead of being entertained. I walk out from movies where such stereotypes abound.
What to do, we are like this only no?