For a single sentence written in response to a direct insult and immediately labeled as a joke by the guy who wrote it, there is no legal strategy that sounds right to me because this is not something that should require a legal strategy to begin with. This situation is preposterous and criticizing the error in legal tactics made by a minor who had no reason to believe he had done anything wrong is completely missing the forest for the trees.

edit: apparently he was 18 at the time, so he wasn't a minor, but I don't feel that makes the situation any less ridiculous