It's been almost 30 years since a Fed chairperson has directly insinuated that stock valuations are pushing historical limits. In December 1996, former Fed Chair Alan Greenspan gave a speech that coined the phrase "irrational exuberance" to describe the nearly parabolic climb of internet-driven stocks, along with the S&P 500 and Nasdaq Composite, following the mainstream adoption of the internet.This six-word phrase, "equity prices are fairly highly valued," is the dagger through the stock market's heart th ...