Comment by asveikau

This phrase was very popular for a good many years, popularized by Greenspan iirc: https://en.wikipedia.org/wiki/Irrational_exuberance

It described the dotcom bubble, but I seem to recall people were applying it to the 2000s housing market too. Tldr it was not a totally uncommon opinion during either of these bubbles to say there was a bubble going on.