Contemptible means deserving of contempt or scorn; contemptuous means expressing contempt or scorn toward someone or something; contumacious means stubborn or willful disobedience toward authority. A law-abiding person may be contemptuous of charlatans and con artists and might refer to such characters as contemptible people. The same person would not call them as contumacious unless they also expressed disobedience toward authority.