“X” isn’t publicly traded. When he bought it, he took it private, so you can’t short it. The ticker symbol X is for the United States Steel Corporation. You could definitely short that, though; it’s entirely possible that it’ll tank just the same because people confuse it with Xitter. Like when that Chinese company that had the ticker symbol ZOOM shot to the moon at the start of the pandemic because people thought it was the video conferencing app (whose symbol was ZM).