It's sad but true in my experience. My thesis advisor makes this a sport, apparently. I learned this after I graduated. One friend explained that my advisor would often call up colleagues at other universities and tell them not to hire particular people. He's apparently known for this habit. It's one thing to provide a recommendation when requested. It's another to routinely campaign against others and provide anti-recommendations.

But he's thrived himself. He's got a swish appointment just outside of Boston.