Today is the anniversary of the birth of Thorstein Veblen. He is not well-known now, and he wasn't particularly well-known when he was alive. Nevertheless, his idea of "conspicuous consumption" is something that many of us understand. Think of it as "signalling".
You and I often buy products to send information to others about our status, our class, our likes and dislikes. We do this because it adds value (or at least we think it does). And it's a concept your students understand. When they make purchases because something is in, hip, cool or whatever the current term is...conspicuous consumption.