I had a very similar conversation with a JW a few months ago. They said everything needed a creator and that creator was God. I said "So *everything* doesn't need a creator, you just said God didn't. Without any evidence, why couldn't I just as easily say that the universe was the thing that didn't need a creator instead of God?"
They said again that everything needs a creator and my response was "Well, no it doesn't. You personally just told me that literally everything needs a creator and then told me that wasn't true. If your god doesn't need one, then you can't claim everything does, and if it's possible to exist without needing a creator, then why can't that thing be the universe? Why is it your god? What evidence do you have that your god exists without having been created? And before you go to the Bible, I can show you 20 other religions that aren't Christian that claim the same about their god, why should I believe your religious claim over theirs? You've no more evidence than them."
They too promised to come back the next week and never did. I ran into them about a month later at a grocer and asked why they hadn't come back. They said they were looking into it.
Slackers.