The act of "smell discrimination" comes into play when you decide by the people who surround you and their physical appearance/demeanour, who it is that created the disgusting smell.
Guy 1: "Dude, something smells like rotten eggs. I think it was that fat hairy guy over there" *Points*
Guy 2: "That's smell discrimination! It could have just as easily been that hot girl in the pink tank top!"