From the Wikipedia article on ad hominem arguments: "Ad hominem (Latin for 'to the person'), short for argumentum ad hominem, refers to several types of argume

From the Wikipedia article on ad hominem arguments: "Ad hominem (Latin for 'to the person'), short for argumentum ad hominem, refers to several types of arguments, some but not all of which are fallacious." [Emphasis added] In particular, pointing out that someone is speaking outside of their area of expertise is a logically valid ad hominem argument.