This time last year, one stock market day trader was making headlines around the investment world.

So convinced was he that stocks go only in one direction - upwards - that Dave Portnoy took to pulling scrabble letters out of a bag and buying a stock that corresponded to that letter.

While some pointed to the irresponsible nature of his actions, others said he was simply exposing the absurdity of stock markets that were being fuelled by waves of cheap money being unleased by the US Federal Reserve.

Stock markets had taken a big hit in the aftermath of the onset of the pandemic globally, but swift action by Central Banks worldwide saw massive amounts of stimulus being poured into the financial system.

Much of it found its way into stock markets which saw them rebounding quickly, eventually hitting consecutive all-time highs.

And it wasn't just institutional investors that were riding the wave.

Day traders - many of whom were working from home or had been temporarily laid off from their jobs - got in on the action, mainly via commission-free trading platforms.

While initially they focused on firms like Netflix, Amazon and Zoom - stocks that were poised to perform well (and did) in lockdown - more recently they've turned their attention to 'less-loved' stocks.

Reddit squad

Wallsreetbets - a community of around 4.5-million-day traders on the social media site, Reddit - has been well known among sections of the investment community for many years.

However, it came to wider prominence earlier this year when the stock of the video gaming retailer, GameStop, came onto its radar.

Some users noted that the stock was trading low and, believing it might have more value, they bought in.

But as more and more buyers came on board, it developed into something of a campaign against the short sellers who were betting on the demise of Gamestop.

The Reddit users were intent on teaching a lesson to those - mainly hedge funds - that they believed were seeking to profit on a brand that was struggling against the backdrop of a pandemic that had shuttered bricks and mortar retailers.

"You're a firm who makes money off of exploiting a company and manipulating markets and media to your advantage," one Wallstreetbets member wrote, directing the comments at Melvin Capital, one of the most prominent GameStop short-selling hedge funds.

"I’m making this as painful as I can for you."

The short squeeze

Short selling is a legitimate practice whereby an investor decides a company's share price is overvalued and likely to fall and it seeks to make money from that move.

Markets provide a way to make that bet.

The investor borrows shares of the company, normally from a broker.

The short seller then quickly sells the borrowed shares into the market and hopes that the shares will fall in value.

If the prices do fall, then the investor buys those same shares back at a lower price.

The short seller then returns the shares to the lender and makes a profit by pocketing the difference.

If they don't fall, then the short seller potentially gets into difficulty.

The higher the share price goes, the bigger the loss the short seller sustains.

GameStop was heavily 'shorted' by numerous funds.

The intention of the Reddit users was to 'squeeze' the funds into a loss-making position.

Hence the 'short squeeze'.

And squeeze them they did. The hedge funds sustained losses into the billions of dollars.

And it wasn't just GameStop. The Wallstreetbets folk turned their attention to other stocks too, including cinema group, AMC, home furnishing retailer, Bed, Bath and Beyond, and - more recently - health insurance company, Clover Health, as well as some other names.

In a phrase that's entered modern day investment lexicon, they've become known as 'meme stocks' - loosely defined as stocks that see dramatic price increases, mostly fuelled by people on social media.

What's wrong with defending a company that's down on its luck?

Admirable as that sentiment is, stock prices are supposed to be broadly reflective of a company's worth and its growth potential.

Short sellers have their place when a company is seen as being inflated in value relative to its performance and they can bring a dose of reality back into the market.

With shares up over 1,500% in January of this year, GameStop was valued at one point in excess of $20 billion.

In reality, the company is worth at most about a tenth of that valuation.

The rally in the share price has been driven by what Paul Sommerville of Sommerville Advisory Markets described as 'the ludicrous nature of certain sections of the marketplace - euphoria mixed with idiocy.'

He pointed to a previous stock trade as a salutary lesson for investors who get swept up in trading meme stocks.

That was the car rental company Hertz, the share price of which rose by 900% as investors snapped up stock after the company had filed for bankruptcy protection.

When the final bankruptcy plan was unveiled, the small-time traders bore the brunt of the losses.

"The 'little guy' gets wiped out," he explained.

"Many of the debtors and large Wall Street firms collect millions in fees and partial repayments while the equity investors that did not know what they were doing get zero."

While the GameStop and AMC scenarios are different - and indeed some retail investors have made significant profits from trading those stocks - the potential for wipe out is just as real.

Aren't they winning against the hedge funds though?

They certainly have caused the hedge funds to retreat in great numbers.

According to figures from Barclays, short sellers have shrunk their positions in heavily shorted stocks by 80% since January, from about $25 billion to just $5 billion.

However, according to Peter Brown of Baggot Investment Partners, it's not just hedge funds that will end up eventually taking a loss on this episode.

Those who get swept up by the wave of buying the stock late in play are putting themselves at risk of big losses on their investment.

He likened the meme stock trade to a pyramid scheme.

"If you buy at $50, you need someone to buy it at $60. At $60, you need someone to buy at $70 and so on. And because the inherent value of the company is somewhere around $2, somebody is going to lose out and it's always the retail investor who gets killed in the end," he explained, referencing the stock of AMC.

"The advice for retail investors is to stay a million miles away from it."

Is it just US based investors that are getting on board?

It is happening pretty much everywhere.

The share trading platform Degiro publishes a monthly index of the most traded stocks on its platform.

In May, the most traded stocks in 10 of the 18 countries in which it operates in Europe was AMC - a recent high-profile target of a short squeeze.

It was the most traded stock in Ireland in the month.

In March, the most traded stock in Europe was GameStop with only two countries - Greece and Hungary - bucking the trend. (Incidentally, Piraeus Financial Holdings and SOS were the most traded stocks respectively in those countries in March).

What next for meme stocks?

It appears that more and more names are getting roped in under the meme stock banner.

The more brands that are subject to a short squeeze, the less effective the practice will be as the force of the buying pressure will become increasingly fractured.

As far as the meme stocks themselves are concerned, in most cases they simply aren't worth the prices being paid and that means that they will inevitably fall.

Paul Sommerville said it is not as simple as the 'David versus Goliath' narrative that has been portrayed in some quarters.

Much of this, he said, is being driven by high frequency computer trades and ultimately by hedge funds battling hedge funds.

"Amateur investors tend to come unstuck in an environment such as this," he warned.

"The smart move is to hold back, take your time and wait for a decent investment opportunity to come to you," he advised.

And remember the adage; If it seems too good to be true, it probably is.