Waiting for a delayed flight when you have a tight schedule is extremely frustrating.

frustrating 是形容词，由动词 frustrate（使沮丧、挫败）加上后缀 -ing 构成，表示"令人沮丧的"或"使人感到挫败的"。这个词描述的是让人感到失望、恼怒或无能为力的状态。