With no substantial recent data for markets to get hysterical about, today was more or less a wash for the S&P 500 Index (SNPINDEX:^GSPC). There was some pressure on equities in the afternoon, though, as a tenuous political situation in Egypt threatens to embroil the country in civil unrest once again. However, the S&P calmly fell just under a point, or less than 0.1%, to end at 1,614. The following three companies weren't so lucky, unfortunately, and finished as some of the worst-performing stocks in the benchmark index.

DaVita HealthCare Partners (NYSE:DVA), which specializes in kidney dialysis services, sank 5.9% Tuesday, ending as the most sold-off stock in the S&P, and for good reason. Late yesterday, a 9.4% -- about three times as steep as the expected amount -- was proposed for Medicare reimbursements for kidney dialysis. The catalysts for the proposed cuts are government reports alleging that Medicare overpaid by more than half a billion dollars for anemia drugs in 2011 alone.

Business equipment and communications company Pitney Bowes (NYSE:PBI) is second on today's list, after plummeting 5.9%. Shares in the company are extremely volatile and fluctuate more than 70% more wildly than the market itself does. After a recent 50% cut in its dividend, the yield still sits at just more than 5% annually, which, for income-oriented investors, can look scrumptious from a distance. The business itself, however, still needs to prove its long-term viability in a world of increasingly digital communications.

Lastly, alcoholic beverage company Constellation Brands (NYSE:STZ) shed 3.6% today. The reason was simple: Its quarterly results were nowhere near up to snuff, whiffing on both earnings and revenue projections. That said, the beverage company, which now focuses mostly on wines, has a major expansion in its future as it readies financing for Mexican brewer Grupo Modelo. Not only were more attractive rates for the acquisition announced today, but the purchase will diversify Constellation's portfolio and make it the third-biggest American beer company.

Fool contributor John Divine has no position in any stocks mentioned. You can follow him on Twitter @divinebizkid and on Motley Fool CAPS @TMFDivine.

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