[...okay, that will honestly probably not have the intended effect - if anything, it seems to please him greatly because ooh, are we doing this now? He likes doing this.]

Ah - a philosophical question! Very unexpected, I'll give you that much!

But to answer your question, I can't! There are many theories that actually say I'm doing exactly that, and it's entirely possible that I'm either hallucinating you right now or you're otherwise not real! You have no way to know that you aren't the only person in the world that actually exists, do you? Not if we're making assumptions based only on what our minds can perceive!

[...he says, like that doesn't sound like an existential crisis in the making.]