The only time I call someone out for slinging insults and launching personal attacks, is when someone uses them as their response, rather than responding to the actual facts/issue at hand.
Example: O'Reilly obtains document proving Pelosi stole Government funds
Response: O'Reilly is an idiot and proven liar
The prof responded to the topic, then injected an insult. He didn't use the insult as his response.