I had a -10x engineer in my team. They refused to test their own work, because that was the tester's job. They sometimes implemented a feature in the wrong place, both technically and functionally, requiring a complete rewrite (and removing code, roll-back was not an option in this tool). They started using float in HTML while we used grid, this caused stuff to be on top of each other.

Unfortunately, this guy played management in a way that caused him to keep getting away with the behavior. Awful person to work with!