What is it?

This is a tactic where negative information about a person is presented before they have a chance to speak, in order to bias the audience against them and their argument. It's a form of preemptive ad hominem attack.

Examples

How to Avoid This

Let people speak for themselves. Judge arguments on their merits, not on preconceived notions about the speaker. Introduce people and their ideas neutrally.

How to Counter This

Point out the attempt to poison the well. 'It seems you're trying to discredit me before I even speak. I hope the audience will listen to my argument with an open mind and judge it on its own merits.'