Nothing, because the guy is probably completely mentally unaware at this point - assuming it's the real biden.

I'd say, "Who are you?"

Thanks for raising the target value of the plane, asshole. But at least my death would be for the common good.

“ The lavatory? Yeah,that door right there that says ‘exit’ “.

"Whoopsie, I really thought it was a mask... <awkward pause> Do you want it back?"