I think you're describing a tipping point - where the association is so strong that it inhibits other uses. The association in this case is "a Prius is a minica

I think you're describing a tipping point - where the association is so strong that it inhibits other uses. The association in this case is "a Prius is a minicab" - which seems to be mostly true in London. I'm sure it's a practical vehicle, since the choice of minicab vehicle is necessarily a very practical one, driven by factors such as Return on Investment, carrying capacity, and finding a vehicle that one can comfortably spend double-digit hours per day inside. But now, we don't want one since it's going to be assumed to be a minicab.