I have already proven that I am a large, extraterrestrial raven. Prove that I am not.

I feel like this is referencing some joke I don't get. But just for shits: Ravens don't have opposable thumbs. If you were a raven you wouldn't be able to use internet-capable devices like a computer or a smartphone.

CorvusBlackthorne · M

@MichaelDemiboy I have opposable thumbs, as I am descended from a mutated species of ravens on another planet. The mutation was caused by a nuclear war which wiped out the dominant species on that planet. You reference only the birds on this planet, while ignoring the fact that I already established that I have traveled across the galaxy to get here.

And the joke, as you put it, is that all of this is illustrating the problem of the burden of proof. The mere fact that something cannot be disproven does not mean it is true.