Finally, today's laggards can feel some sort of camaraderie with the rest of the market, which declined pretty markedly in its own right. Just one trading day after boasting gains in all 10 industry groups, the S&P 500 Index (SNPINDEX:^GSPC) saw losses in all 10 industries today. The following three stocks represent some of the worst of the worst performers in S&P 500 today.

Oil and natural gas driller Nabors Industries (NYSE:NBR) lost 3.6% in Monday trading, falling on a combination of factors. The main reason shares struggled today was simply the bearish overall market environment, which contributed to a decline in oil prices, which now sit around $96 per barrel. Large bond investors are also worried about a possible leveraged buyout of the energy company, which could result in a downgrade of its corporate debt. 

Business equipment maker Pitney Bowes (NYSE:PBI) which led the index's laggards on Friday, fell a further 3.5%, after slipping more than 4% at the end of last week. Today's decline fell in line with the overall theme of the day, which seemed to be taking profits; the stock rose more than 20% Thursday after exceptional quarterly results. In so many words, Pitney investors experienced a Groundhog Day-esque deja vu day of trading that mimicked the rationale behind Friday's stumble.

Advanced Micro Devices (NASDAQ:AMD) rounds out the list of today's losers, falling 3.1%. The chipmaker didn't suffer from much else today other than momentum that seems to be going in the wrong way. The stock has now lost more than 10% in the last five days and over 40% in the past six months as investors anxiously wait to see how AMD will adapt to the move from PC to mobile devices.