(Strategies) WorldCom, Lucent Technologies, Wachovia and Rivian Automotive: These companies are members of a dubious group, the worst stock market investments of the last century. That lowly status is documented in a long-running study that has gotten far more attention for its depiction of the century's best stocks. But it suggests that the most dangerous times for investors are when the market is high -- and we may be in such a time right now.