Okay, for this question, you have to go about reasoning 'Objective Truths.' Since you are trying to prove the fact that you do not necessarily exist, the way you would go about that argument would be to present analogy. Say a man is walking down the street eating a banana. Another man, who happens to be a crack addict (or any other mind-altering drug addict) walks up to the first man and strikes up a conversation:
Druggy: What are you doing with that gun!?!
Man: What gun, I am eating a banana.
Druggy: No, that is most definitely a gun. Why are you pointing that in your mouth!?
Man: No sir, this isn't a gun, this is a banana.
Druggy: Someone call the police! This guy is trying to kill himself!
Given this unlikely scenario, who is correct? If you say the man eating the banana, how did you come to this conclusion? What if the man eating the banana was on drugs, and the Addict was merely trying to get the man to take the gun out of his mouth. You see, the way we perceive reality (perception of existence) is faulty, because all reality is is just a compilation of electrical signals stimulated to the brain. How do you know if you really exist, or if your whole life is just a conglomerate of memories some drug addict or RPG player thought up of while strung out on their respective addictive substances? And if someone pulls out that "I think, therefore I am" playing card, characters in books think all the time, it doesn't mean they exist.
Edit: I re-read this, and the explanation is a little bit murky at the end, so, Philosophy-mobile AWAAAYYYY: My argument would be analyzed as being based on characters in novels or movies or video games, and one would be right. The character, the flesh and blood and sword and shield and emotions and prerogatives, all in all, is not real. That is the truly unreal thing of this world: Imagination. If the equation supports all real numbers, what doesn't it support? Imaginary numbers. That really is the only place you can take refuge in this argument for. What if we are all just characters in someone's book? How could we know it if Frodo didn't? Now using this argument, people will throw out at you phrases such as "But Frodo is real, I see the letters right there on the page!" To counter this: Ask the question "Are you just letters on a page then?" It's foolproof!