Acknowledge it right away and try to explain yourself. That might sound like this: "That came out a lot harsher than I meant it to. I was really trying to say that I'm confused about how the market might react to an electric toe-jam removal kit. But I'm very excited about joining a team that thinks so creatively." Yes, that might work.
Ask for a five-minute restroom break, then try to charm your way to safer conversational ground. Here's an example of the return from the break: "Thank you for agreeing to that short break. I was surprised by the originality of your new toe-jam product, and I frankly needed a minute to absorb it. Now that I've thought about it more, I can really see some interesting possibilities for the marketing. Can we spend a minute talking about that so I can understand more fully how I could contribute to those efforts?"
Bulldog through. If you really want to make an impression, stand your ground and make the point with even more emphasis, then explain how you can help salvage their sad idea. You really, really shouldn't imagine this actually working, but on the other hand, it's a viable alternative if you can't imagine shilling the product either.
Stay calm and carry on. As with any conversational blooper, you always have the option of ignoring it. Going with the theory that the more you emphasize it, the worse you'll make things, you can simply continue with the interview as if nothing happened. Of course, if you don't get the job, you'll always wonder if you did the right thing, but that's the kind of second-guessing you'd do after almost any interview.
What if you don’t realize until after the interview that you massively misspoke? Again, if the affront could be taken personally, a clarifying and apologetic note will have the most impact. But here’s the problem: Do you really want to enshrine your mistake in permanent, written form? Tricky.
If the blooper was more professional than personal — we’re back to the unfortunate product launch as an example — a well-crafted follow-up letter might be just the ticket. Just be sure to reference your conversational error only briefly while presenting a paragraph or more on your newfound enthusiasm for the idea.
Which brings us to a final point to consider: It’s possible that your misplaced remarks weren’t even noticed by your interviewers. If you think you could be fretting over something that didn’t register with others in the room, then follow up with the interview as you normally would: cheerfully, optimistically and with persistence. But remember this: If you manage to convert this situation into an offer, you will have to face that product idea again, and you’ll have no one to blame but yourself.