I'm going to vote the same way most of my fellow consultants above have:
[x] You DON'T TELL A CLIENT "I Told You So."

...Not even if they "deserve it" --which OF COURSE THEY DO. Whomever said "the customer is always right" was wrong. Statistically, the [IT] customer is almost NEVER right. But he'll always be the customer and there's a certain convention of behavior we "vendors" are expected to maintain. We're the ones getting the grief but that's supposed to trade-off with the fact we're also the ones getting the check.