NEW YORK ( TheStreet) -- In a rare somber moment on his "Mad Money" TV show, Jim Cramer issued a stern warning his viewers that "those who forget history are condemned to repeat it." He said while his job on "Mad Money" is to offer hope and opportunity, it's also to issue caution when warranted, and today is one of those times. Cramer was of course talking of the meteoric rise of the social network LinkedIn ( LNKD), which debuted today at $45 a share and soared to $122 a share before settling out at $94. He said this lightning bolt of an IPO has made a mockery of the capital markets and this sort of deal is the enemy of the individual investor. Cramer said the investment bankers that brought this deal public knew exactly what they were doing, using the same tactics employed during the dot- com bubble of 2000. He said only a sliver of stock, just 7.84 million shares, were brought to market, a fraction of what was needed to satisfy demand. This led to mutual funds and others to bid the stock up in the open market, artificially inflating the price far beyond where it deserves to be. "These guys knew exactly what they were doing," he explained. But just as in the dot-com bubble, Cramer said this story doesn't end well. He said LinkedIn now sets a precedent, and a plethora of deals will now be headed down the pike, all employing the same tactic, each deal being worse than the last. "We are playing with equity fire here," said Cramer, "and that equates to portfolio arson." Cramer said the regulators are looking the other way, leaving the venture capitalists, the only ones to make money on these deals, to jump for joy. Cramer said he's seen this game before, as he founded TheStreet ( TST) right in the middle of the dot-com bubble, and was there to pick up the pieces. "There were 300 companies that went public between 1999 and 2000," said Cramer, "only a handful are still around today." Cramer's bottom line: The LinkedIn deal was not good for the markets, and it certainly isn't good for your portfolio. "It's all downhill from here," he concluded.