Ouch. I have a much, much more pleasant memory involving my grandma's belief in creationism. I'm not sure how the topic came up, but she raised this point: "If evolution is true, then why aren't there Neanderthals and other hominids running around today?" (Not phrased exactly like that, but that was the upshot of it.)
Now the thing is, this is not an illogical question in my mind, as scientists are working to understand exactly why we don't see Neanderthals, Denisovans, Flores men, or any of them running around in genetically pure/recognizable forms today. And I personally think it would be really interesting to imagine a world where that was still the case. Hoooooly shit, just imagine the crazy shit that would go down between the various humanities. O_O If I were being really optimistic I'd say that we would simply have a more expansive, generous definition of what shared "humanity" is, but considering the stupid nitpicking we do to each other with good ol' Homo sapiens sapiens and our little genetic remnants of the other species...my optimism takes one look at that, withers, and dies.
But I just looked at my grandma and said, with a perfectly straight face, "But Grandma, there are Neanderthals EVERYWHERE!!!!" (This was before we had proof of many humans carrying their DNA so I was going for something else.
Instead of a stupid argument, we both managed to have a really good laugh at that line.