The furious behaviour of an angry man is more likely to exasperate us against himself than against his enemies.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“This, however, does not hold universally, or with regard to every passion. There are some passions of which the expressions excite no sort of sympathy, but, before we are acquainted with what gave occasion to them, serve rather to disgust and provoke us against them. The furious behaviour of an angry man is more likely to exasperate us against himself than against his enemies. As we are unacquainted with his provocation, we cannot bring his case home to ourselves, nor conceive any thing like the passions which it excites. But we plainly see what is the situation of those with whom he is angry, and to what violence they may be exposed from so enraged an adversary.” source