Comment 22 by TheRationalizer :

Dear young Earth creationist. If the universe is really 10,000 years old then why are we seeing the death of a star that occurred 13 billion years ago. Believing god lined up photons for us so that we can see them is one thing, but why would your young-Earth god show us that a star exploded 13 billion years before it could possibly have existed? :)

When debating with creationists, that is my favourite example which I use to explain what is meant by "falsifiability" - arguably the most important pillar of science (and the F in "FiLCHeRS"). That is, in order for a statement to be testable (and have meaning), you must be able to think of evidence that would disprove it. (The claim might survive the test and live for another day, but it still needs to be testable.)

The argument goes as follows. If the universe was made 10,000 years ago, then the light from stars that are 10,000 light years away should only now start to reach us - we should see new stars popping into the sky every night, or at least every month - and each new star would be progressively further away. This doesn't happen, and if your excuse is that some stupid god created the stars with their light rays already stretched to earth, that excuse is not falsifiable. That is, there is no evidence that could conceivably disprove it, because if you allow gods to tamper with the evidence then there is no such thing as evidence. The concept of Falsifiability is equivalent to saying that "the evidence must matter".

At that point I ask them: If light rays cannot be trusted because they are being manipulated by some stupid god, then why do they look at their bank statement or look before crossing the road?