Even the best persons have “one of those days” when frustration boils over into anger. Saints are not even immune from this.
One of the most famous examples of this involves St. Teresa of Avila. She was on her way to visit one of the 15 Carmelite monasteries she founded. St. Teresa fell off her donkey, landed in mud, looked up to heaven and said to God, “If this is how You treat Your friends, no wonder You don’t have many.”