Haha is used for sarcasm or to denote a joke. The fact is that your "joke" was based on an esoteric and strange assumption that "I'm already dead" would become "I'm going to kill myself".
You still have not answered how that is supposed to make sense with the simple addition of "haha".
Sure the "haha" means you're joking, but all that means is "ye im not dead obviously"
Or it could be a hint of a nervous laugh to make the "im already dead" funnier. If I were to say "I'm severely depressed, haha" in a context where it is obviously a joke then it is easy to interpret it to mean "I'm not severely depressed" or that I am making a joke of my depression.
You saying "I'm already dead, haha" just means you're making a joke of the fact that you're already dead. It does not change the literal meaning of the words spoken. It changes the minutia of how they are interpreted, not the entire fucking sentence.
God, abbos really are fucking stupid aren't you.