Yes you can short a stock under 5 dollars and it depends on your broker in many occasions for specific stocks, sometimes you will either have to call their customer service for online brokers or fill out certain paperwork. Shorting stocks under 5 dollars is sometimes all people do, especially with paid pumps and scams they wait till the stock breaks out from promos and PRs and short it and sit back and wait till it tanks and also many people base their shorting on the fact that a great percentage of these penny stocks never surmount to much and fail so the likelihood of the price falling or tanking is greater than it risimh or breaking out and factor in the amount of Times if a stock does breakout up, how quickly it collapses after either selloffs or end of promos