There are basically three ways to destroy someone's image.

1. Attack their competence: Show the audience that your subject doesn't know what they are talking about. Show them your subject's incompetence by pointing out incoherences in their speech. By attacking competence, you point out the lack of legitimacy.

2. Attack their Character: Show the public the antipathic part your subject's character. Highlight their arrogance. Highlight their lack of ethics. Show the audience that what your subject is doing doesn't come from passion, but, from greed.

3. Hit under the Belt:

 Show the audience parts of the intimate life of your subject. Everyone has dirt, everyone has had embarassing moments in their private life. Make that public.