When the curtain closes on 2021 in a tad over six months, there's little question this year will be remembered for the rise of the retail investor. Even though retail investors have been putting their money to work in stocks for more than a century, their collective efforts have moved markets like never before in 2021.

Without getting too far into the weeds, they have been using social media platforms like Reddit as a staging ground to rally the troops and seek out stocks with very high levels of short interest. Retail investors have then been purchasing shares and out-of-the-money call options in order to effect a short squeeze -- when pessimists head for the exit at the same time. Short squeezes are quick-occurring events, but they can lead to eye-popping run-ups in the price of a stock.

However, not all heavily short-sold stocks should be bought by investors. In many instances, a large short position exists because the underlying business model or industry is broken, or management is failing on multiple levels. The following five heavily short-sold stocks fit that bill, and they should all be avoided like the plague.

A blue street sign that reads, Risk Ahead.

Image source: Getty Images.

Sundial Growers

Canadian marijuana stock Sundial Growers (SNDL 3.08%) has been a common target for short-sellers for over a year. Even with its minuscule $1 share price, almost 268 million shares were held short as of May 28. But there's a very good reason for folks to be pessimistic: Sundial's management team has been a disaster.

Beginning in October 2020, management began raising capital to strengthen the company's balance sheet. Although all debts have now been paid off, the equity offerings have just kept coming. In the span of seven months and one week, the company's outstanding share count ballooned from 509 million to 1.86 billion. Existing shareholders have been buried by management's ill-advised capital raises, and with 1.86 billion shares outstanding, the company has virtually no chance of ever producing meaningful earnings per share.

Making matters worse, Sundial Growers' cannabis operations have gone up in smoke. Management made the decision to switch away from wholesale marijuana to higher-margin retail cannabis. Unfortunately, this shift has caused sales to plummet. Whereas most North American pot stocks are thriving, Sundial is stuck in reverse.

An electric vehicle plugged into a charging station.

Image source: Getty Images.

Blink Charging

Electric vehicles (EVs) and ancillary EV players could be some of the biggest winners over the next decade. But short-sellers are pretty convinced that Blink Charging (BLNK 4.76%), a provider of EV charging accessories and networks, won't be one of them. More than a third of the company's float (its tradable shares) are currently held short.

Arguably the biggest red flag for Blink Charging is that the company doesn't look to be investing any of its more than $230 million in cash and marketable securities into research and development (R&D), the cornerstone growth driver of the EV industry. Without R&D, there's absolutely nothing that separates Blink Charging from its competition.

Just as unnerving is the fact that Blink's sales are dubiously low for a company sporting a $1.7 billion market cap. During the first quarter, the company brought in only $2.2 million in revenue, with product sales driving the entirety of its year-over-year growth. The combination of charging service revenue and network fees actually declined from the pandemic-impacted first quarter of 2020. With Blink still many years away from being relevant, it makes for an easy stock to avoid. 

A small stack of Bitcoins used as bait in a mouse trap.

Image source: Getty Images.

MicroStrategy

To some, MicroStrategy (MSTR 3.38%) CEO Michael Saylor is a hero or revolutionary for his willingness to add Bitcoin (BTC -1.09%) to his company's balance sheet. But I'm more inclined to side with the short-sellers who find his actions reckless.

It's one thing for a company to use a percentage of excess cash to purchase Bitcoin to carry on the balance sheet. What Saylor did was issue over $2 billion in debt -- capital that MicroStrategy doesn't have -- to purchase additional Bitcoin. According to the company, it owns 105,085 Bitcoin tokens at an average price of $26,080. Taking into account that Bitcoin has had three separate drawdowns of at least 80% over the past decade, this all-in strategy could easily backfire

To boot, Saylor has seemingly ignored the company's business-intelligence segment, which is working on a six-year streak of declining sales. He's effectively turned MicroStrategy into a leveraged shell company that's completely dependent on an external factor (Bitcoin), rather than innovation. This looks like a recipe for disaster.

Former CEO Steve Burns standing next to a Lordstown Endurance prototype EV truck.

Now-former CEO Steve Burns standing next to an Endurance prototype EV truck. Image source: Lordstown Motors.

Lordstown Motors

In case you didn't get the memo the first time around, EVs are a really popular place for investors to park their cash. But investors have a tendency to overestimate how quickly new technology will be adopted, and they sometimes overlook that not all industry players will succeed. That could well be the case for the heavily short-sold electric truck company Lordstown Motors (RIDE -1.70%)

In a span of six days in June, Lordstown has: 

Building an EV company from the ground up is costly, time-consuming, and not without speed bumps (just ask Tesla). With a new management team taking the wheel and the company's cash situation perilous at best, it's not even clear if Lordstown will survive. Though the EV industry will have long-term winners, this company is easily avoidable for the time being.

A couple eating popcorn and drinking beverages while watching a film in a movie theater.

Image source: Getty Images.

AMC Entertainment

Lastly, as if there were any doubt, heavily short-sold movie theater chain AMC Entertainment Holdings (AMC 3.96%) should be avoided like the plague. While Reddit traders would like to believe that manipulation is the reason behind AMC's high short interest, it actually has to do with AMC's poor operating performance and the mediocre outlook for the theater industry as a whole.

For the past 19 years, ticket sales for the movie industry have been in a fairly steady decline. This is likely to continue with streaming services pushing traditional theater chains for exclusivity, and select studios shortening the exclusivity time frame of films at theaters. Even with a larger share of the theater market, AMC's pie continues to shrink.

The bigger issue for AMC is that the performance of its stock doesn't come close to matching its underlying operating results. People might be returning to the theater, but AMC is still burning through a lot of capital, and it's many, many years away from turning a profit. That's a problem for a company with more than $5.4 billion in outstanding debt -- and the pricing of its 2027 bonds shows it.

AMC is being driven by hype and misinformation, and it's not clear how long this irrationality will last. One thing that is clear is pump-and-dump schemes like this one always end poorly.