Objection 1. It would seem that reviling does not arise from anger. For it is written (Proverbs 11:2): "Where pride is, there shall also be reviling [Douay: 'reproach']." But anger is a vice distinct from pride. Therefore reviling does not arise from anger.
Objection 2. Further, it is written (Proverbs 20:3): "All fools are meddling with revilings [Douay: 'reproaches']." Now folly is a vice opposed to wisdom, as stated above (Question 46, Article 1); whereas anger is opposed to meekness. Therefore reviling does not arise from anger.
Objection 3. Further, no sin is diminished by its cause. But the sin of reviling is diminished if one gives vent to it through anger: for it is a more grievous sin to revile out of hatred than out of anger. Therefore reviling does not arise from anger.
On the contrary, Gregory says (Moral. xxxi, 45) that "anger gives rise to revilings."
I answer that, While one sin may arise from various causes, it is nevertheless said to have its source chiefly in that one from which it is wont to arise most frequently, through being closely connected with its end. Now reviling is closely connected with anger's end, which is revenge: since the easiest way for the angry man to take revenge on another is to revile him. Therefore reviling arises chiefly from anger.
Reply to Objection 1. Reviling is not directed to the end of pride which is excellency. Hence reviling does not arise directly from pride. Nevertheless pride disposes a man to revile, in so far as those who think themselves to excel, are more prone to despise others and inflict injuries on them, because they are more easily angered, through deeming it an affront to themselves whenever anything is done against their will.
Reply to Objection 2. According to the Philosopher (Ethic. vii, 6) "anger listens imperfectly to reason": wherefore an angry man suffers a defect of reason, and in this he is like the foolish man. Hence reviling arises from folly on account of the latter's kinship with anger.
Reply to Objection 3. According to the Philosopher (Rhet. ii, 4) "an angry man seeks an open offense, but he who hates does not worry about this." Hence reviling which denotes a manifest injury belongs to anger rather than to hatred.
Source: Summa Theologica (New Advent)