Whenever someone publicly claims not to be able to give a speech, or talks about how ineloquent or rough-spoken they are, they're lying. Run for the hills, or resign yourself to giving them anything they want. This Stock Phrase can be traced as far back as Plato, who put it in the mouth of Socrates at his trial. This is the standard tactic of the Simple Country Lawyer, and often leads naturally into a Rousing Speech. Mirror Monologue or other technique can be used to show them practicing beforehand -- often with the line about not being able to give a speech.