PepsiCo has badly lagged the S&P 500 over the last year. Does this represent a buying opportunity?When a stock doesn't perform well, it's natural to ask whether you should buy, hold, or sell the shares. After all, it could present an opportunity, or the market might sense there are continuing challenges with the company.PepsiCo's (PEP -1.99%) shareholders face such a decision. The share price has badly underperformed the market, falling 1.5% over the past year even as the S&P 500 gained 26.6% during this ti ...