忍无可忍 is a fixed four-character idiom that literally means 'to endure but cannot endure' — i.e., to reach the limit of one's patience, to a point where one can no longer tolerate something. It functions as a verb phrase (v.p.) and often appears in patterns like 到了忍无可忍的地步 ('have reached a point of being beyond endurance') or as a standalone predicate. The idiom conveys a strong emotional state of exhaustion from persistent annoyance, unfairness, or provocation.