When you are among a large group of people (Usually people you don't know, like at
school or a train station or a store) and suddenly the
air becomes occupied by a nasty odour.
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.
(In a store)
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!"