And having been hymned aloud by Vasistha and others,—overflowing with clemency, thou hast grown haughty,—and it is for this reason that thou insultest even me in this way. Who is there in all these three regions that beholding the frowning face of mine furnished with flaming matted locks,—can keep off fear; forgive I will not. What then is the use, O thou of an hundred sacrifices, of thy expending much speech. Thou again and again puttest thyself to useless trouble in thus beseeching me".

In plain words: Durvasa says the praise and kindness of sages like Vasishtha made Indra vain enough to insult him. He says nobody can face his angry face and fiery matted hair without fear. He will not forgive, so Indra's pleading is useless.