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.
Tim Seymour of EmergingMoney.com said that we're not "terribly bubblicious in terms of the S&P," but added that "you need to be concerned." Ritholtz Wealth Management's Josh Brown expressed similar sentiments, saying, "I was much more comfortable being bullish when people hated stocks.… But there's a lot of room to make money."
Dennis Gartman of The Gartman Letter offered one way to make money: shorting bonds. Addressing long-term U.S. Treasurys, Gartman said he saw "a massive top … I think you have to be selling the bond market at the long end of the curve."
(Read more: Dennis Gartman sees 'massive top' in bond market)