What the Fallacy?!
Ad Hominem
The Fallacy
Attacking your opponent's character or personal traits in an attempt to undermine their argument.
Why it's wrong
Ad hominem attacks can take the form of overtly attacking somebody, or more subtly casting doubt on their character or personal attributes as a way to discredit their argument. The result of an ad hominem attack can be to undermine someone's case without actually having to engage with it.
Example
During the debate on environmental policy, the candidate ignored the scientific data presented by his opponent and instead argued that no one should listen to someone who wears such terrible ties.