The ad hominem fallacy occurs when someone attacks the character or personal traits of an opponent instead of addressing the argument itself. This tactic diverts attention from the actual issue and undermines rational debate. For example, if Person A argues for a policy and Person B responds by criticizing Person A's personal life, Person B is committing an ad hominem fallacy. This fallacy can take various forms, such as name-calling or questioning someone's motives. It is important to recognize ad hominem attacks in discussions, as they can hinder constructive dialogue and prevent a fair evaluation of the arguments presented.