"Do not swear whether by the Creator, or any creature, except truthfully, of necessity, and with reverence" (Spiritual Exercises, 38).
Every good Christian ought to be more ready to give a favorable interpretation to another's statement than to condemn it. But if he cannot do so, let him ask how the other understands it. And if the latter understands it badly, let the former correct him with love. If that does not suffice, let the Christian try all suitable ways to bring the other to a correct interpretation so that he may be saved.