BALTIMORE (Stockpickr) -- We're halfway though 2015, and investors don't have much to show for it. Year-to-date, the big S&P 500 index is about 0.6% lower than it started, which means that you'd have been better off stuffing your cash in your mattress back in January than investing in stocks.

And it gets worse. Many investors don't realize it, but the S&P has actually been a pretty lousy proxy for "the stock market" in 2015. While the big index is just shy of breakeven, almost a third of the individual stocks in the S&P are actually down 10% or more in 2015. Put simply, a big chunk of the market looks toxic right now -- and the toxic stocks are ones that you might even already own.

With that in mind, today we'll take a technical look at five big toxic stocks to avoid this summer.

Just to be clear, the companies I'm talking about today aren't exactly junk. By that, I mean they're not next up in line at bankruptcy court. But that's frankly irrelevant; from a technical analysis standpoint, sellers are shoving around these toxic stocks right now. For that reason, fundamental investors need to decide how long they're willing to take the pain if they want to hold onto these firms in the weeks and months ahead. And for investors looking to buy one of these positions, it makes sense to wait for more favorable technical conditions (and a lower share price) before piling in.

For the unfamiliar, technical analysis is a way for investors to quantify qualitative factors, such as investor psychology, based on a stock's price action and trends. Once the domain of cloistered trading teams on Wall Street, technicals can help top traders make consistently profitable trades and can aid fundamental investors in better entry and exit points.

So without further ado, let's take a look at five "toxic stocks" you should be unloading.

Brookfield Property Partners

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Up first is commercial property company Brookfield Property Partners (BPY) - Get Report. 2015 hasn't been a very good year for shareholders in this $6 billion real estate stock. Since shares peaked back in February, Brookfield has shed more than 16% of its market value, woefully underperforming the big market averages.

Even more selling could be on the way in Brookfield Property Partners this summer. Here's why.

Brookfield is currently forming a descending triangle pattern, a bearish continuation trade that's formed by downtrending resistance up above shares and horizontal support to the downside (in this case at $22). Basically, as shares of Brookfield have bounced between those two technically important price levels, this stock has been getting squeezed closer and closer to a breakdown below our $22 price floor. When that happens, we've got a pretty major sell signal.

Relative strength, at the bottom of the chart, is an extra red flag in Brookfield right now. That's because our relative strength line has been in a downtrend since February, an indication that this stock isn't just losing steam here, it's also significantly underperforming the rest of the market pretty materially. If $22 gets violated, you don't want to own this stock anymore.

American Express

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We're seeing the exact same price setup right now in shares of American Express (AXP) - Get Report. The financial sector giant has been under pressure for all of 2015, and the descending triangle setup this summer is threatening a bigger breakdown in July. For AmEx, the breakdown level to watch is $76.

Why all of the significance at $76? It's not magic. Whenever you're looking at any technical price pattern, it's critical to keep buyers and sellers in mind. Patterns such as the descending triangle are a good way to quickly describe what's going on in a stock, but they're not the reason it's tradable. Instead, it all comes down to supply and demand for AmEx's shares.

That $76 level in American Express is a spot where there's previously been an excess of demand for shares; in other words, it's a price where buyers have been more eager to step in and buy shares at a lower price than sellers were to sell. That's what makes a breakdown below support so significant -- it means that sellers are finally strong enough to absorb all of the excess demand at the at price level.

Keep a close eye on that $76 price in American Express. If sellers can knock out that level, a whole lot of downside risk opens up.

For another take on American Express, check out "Stock Charts Show American Express Could Be a Buy."

Maxim Integrated Products

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$9 billion semiconductor stock Maxim Integrated Products (MXIM) - Get Report has actually been faring pretty well in recent months. Since shares bottomed last fall, this stock has managed to tack on almost 25% to its share price, beating the S&P 500 by more than double over that same timeframe.

But investors who own Maxim might want to think about taking some gains off the table this summer. Shares are starting to look "toppy" here.

Maxim has spent most of 2015 forming a pretty textbook double top pattern, a bearish reversal setup that looks just like it sounds. The double top is formed by a pair of swing highs that peak at approximately the same level. The sell signal comes on a violation of the trough that separates those two tops. For Maxim ,that's the $32 support level on the chart.

Momentum, measured by 14-day RSI, adds an extra red flag to the price action in Maxim. Our momentum gauge has been in a downtrend since last fall, making lower highs on each of the tops in Maxim's reversal pattern. That's a bearish divergence that indicates buying pressure is weakening. If $32 gets violated, then it's time to sell.

Baidu

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It's tempting to think that $64 billion Chinese web company Baidu (BIDU) - Get Report is skirting the selloff that's been happening in Chinese stocks over the last couple of weeks. After all, while the big iShares China Large-Cap ETF (FXI) - Get Report is down more than 16% in the last month, Baidu is has given back less than half that. But that "less bad performance" doesn't change the fact that Baidu looks toxic right now.

The price pattern in Baidu is about as simple as they get. Since last fall, this stock has been bouncing its way lower in a well-defined downtrending channel, swatted down on every test of trend line resistance. Every test of the top of Baidu's price channel has been a great selling opportunity, and as shares come up off of the bottom of their price channel, it makes sense to sell the next unsuccessful test of resistance.

Waiting for that bounce lower before clicking "sell" is a critical part of risk management for two big reasons: It's the spot where prices are the highest within the channel, and alternatively it's the spot where you'll get the first indication that the downtrend is ending.

Remember, all trend lines do eventually break, but by actually waiting for the bounce to happen first, you're confirming that sellers are still in control before you unload shares of Baidu.

Lockheed Martin

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Last up on our list of toxic stocks is $60 billion defense contractor Lockheed Martin (LMT) - Get Report. Lockheed is another stock that's starting to sour after a pretty good long-term price run. In the last 12 months, Lockheed Martin has generated price returns of 22%, making it a major outperformer versus the S&P's weak 4.3% gain. But it's time to think about taking gains on Lockheed this summer. Shares look "toppy" in the long-term.

For most of 2015, Lockheed Martin has been forming a head and shoulders top, a setup that indicates exhaustion among buyers. The pattern is formed by two swing highs that top out at approximately the same level (the shoulders), separated by a higher high (the head). The sell signal comes on a move through this stock's neckline, currently at $185. If that $185 level gets violated, look out below.

Remember to be reactionary when you're looking at Lockheed Martin's chart (or any of the other toxic stocks on this list, for that matter). After all, technical analysis is a risk management tool, not a crystal ball. That means that downside in Lockheed Martin doesn't become a high-probability trade unless $185 gets violated.

On the flip side, a move above the right shoulder at $195 would invalidate the head and shoulders top. Either way, if you have a stake in this stock, it's a very good idea to keep a close eye on that $185 level this summer.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.