A toxic combination of cash burn and equity dilution could leave a hole in your investment portfolio.Penny stocks are shares in companies that trade for less than $5.00 per share. With a current price of $6.67,AMC Entertainment isn't far from that mark. And while the stock might look like a good deal, it is cheap for a reason. Let's explore why the struggling movie theater operator looks poised for more downside over the long term.Profitability challenges and weird managerial decisionsWe all know the COVID-19 pandemic devastated in-person entertainment venues like movie theaters, which saw their locations closed for much of 2020 and 2021. Now that the industry is back on its feet, sales are soaring -- but profitability has been slower to return. AMC's third-quarter earnings repor