First of all, what is it?

"Irrational exuberance" is a phrase used by the then-Federal Reserve Board Chairman, Alan Greenspan, in a speech given at the American Enterprise Institute during the stock market boom of the 1990s. The phrase was a warning that the market might be somewhat overvalued.

http://en.wikipedia.org/wiki/Irrational_exuberance

What does that have to do with sports betting? Irrational exuberance creates a situation like what we saw in the last Spurs/Grizzlies game. First, the game started as a pick and moved to Grizzlies -2 which was very reasonable, imho. However, with the Grizzlies up 10 at halftime the Spurs were only 2 point favorites for the second half. That made the new line for the game Grizzlies -8.

I think that's irrational exuberance, Grizzlies -8 was not a rational line but half the money or so ended up on that line.

It's just like when people were buying stock in internet companies with no earnings at $100 or more per share. It's irrational exuberance and it should be faded in the stock and sports betting alike, imho.