anecdotal but I faced a similar situation. I explained it was a bad idea in a public meeting because it seemed unethical which could hurt our brand longer term.

Fast forward a few weeks and we are testing whose ads are better. Fake testimonial ads are beating mine out until one person comments that they think the testimonial is faked because he had used a common colloquialism and capitalization system. I flag this in our slack channel and he says it's no big deal and deletes the comments from the user on the ad. Our audience evidently didn't play to that and went to a public review site and put up a screen shot as well as went to the FTC with an deceptive act in advertising and reported it on facebook which got our account banned.

In the end he got severely reprimanded and I was given a sort of veto power on his bullshit. In the end the best you can do is give the person enough rope to hang themselves with - especially if your boss is under a presumption he is a genius.