Federal Reserve Chair nominee Janet Yellen testifies during her confirmation hearing Nov. 14.

The traders kicked off a big week of CNBC's "Fast Money" by addressing increasingly mainstream concerns of a bubble in the equity markets.

With the S&P 500 up more than 23 percent in 2013 and stocks hovering near all-time highs, the "Fast Money" crew reacted to a number of newspaper headlines and bubble quotes from the likes of Bill Gross and other Wall Street heavyweights.