Someone makes an unfair remark, and the urge to reply harshly is immediate. عِنْدَ الْغَضَبِ locates the moral test precisely when anger arises, not only when everyone is calm. Restraining an impulsive reaction and stating the truth at a suitable moment is not cowardice.
Example 1: During disagreement, keep one's voice and words measured instead of humiliating the other person.
Example 2: If a heated argument could become unsafe, pause the exchange and address it in a safer way.
Self-control does not require accepting injustice. One can protect rights while responding with restraint and fairness.