I'll take a blind, silly stab at the phrase:

If a person's all wet, he's out-to-lunch, not on the right track, born yesterday.

And, if born yesterday, why not today? And if today, why not just now? And if born just now and extraordinarily naive about the workings of the world, then he's all wet as though just born.

Now, I know this is probably incorrect, but thought I'd throw a little absurdity into the etymological pool, in which I'm probably all wet.

Best regards,
WetWind