How would they be able to sue him? If you killed yourself they’d have no way of knowing that was why, and even if they figured out that was the reason you killed yourself, it’s not evidence of any wrongdoing. He made a joke that wasn’t even targeted towards you. Even if he actually said “u/Destroyed1silence, you should kill yourself because you deserve to die and everyone wants you dead” or something malicious like that and there was proof that you read the comment before you died, they still wouldn’t have enough info to track him down and it’s hardly grounds for a lawsuit. If you really feel like you might kill yourself because of a comment online you need to go offline and get some help.