I had a PM who pushed us to A/B test _everything_. We hired a new graphic designer who suggested that we change our product links from ALL CAPS to Title Case (a very popular idea on the team, and his first real suggestion after a few weeks with us), and she insisted that we A/B test it first. It felt like an insult to him, and a dumb test since title case looked way better.

The three key outcomes I observed from the relentless A/B testing were UI antipatterns, team burnout, and a well-attended conference talk about "how we ran 105 A/B tests in a year, and what we learned".