This statement in Mark 16:15 is provably false:
And [Jesus] said to them, "
Go into all the world and preach the gospel to the whole creation.
He who believes and is baptized will be saved; but he who does not believe will be condemned.
And these signs will accompany those who believe: in my name they will cast out demons; they will speak in new tongues; they will pick up serpents, and if they drink any deadly thing, it will not hurt them; they will lay their hands on the sick, and they will recover.
Well, it may not be directly provably false but as soon as you refuse to drink Draino, it's proven false.
Or, less personal, as soon as Cary Jacobs, dying of Huntington's Disease as of 4/23/2009, fails to RECOVER after you have laid on your hands, it's proven false.