Not too long ago, I was assigned Review on a clearly vibecoded PR. It was for a feature that parsed hourly values from a csv file and put them into the Database. Easy enough at first glance, just loop through the hours of the day and grab the value for each hour, with an error if your file doesn’t contain all the hours of the day. But for some reason my coworker not only decided to introduce a whole new “hour of the day” type to loop over instead of looping over numbers, but that type explicitly contained 25 values. It was the numbers 0 to 24. There was even a comment next to it saying that it had 25 values. All test cases were green too, because the test data was generated specifically to satisfy the tests. I had to explain to a grown ass adult that the day only has 24 hours and it wouldn’t work because there will never be a value for “24:00” in the real data. That specific coworker already made really stupid mistakes before AI was a thing, but at least those mistakes were easy enough to spot and didn’t secretly propagate themselves through thousands of lines of code.