erratic
adjective uk/ɪˈræt.ɪk/ us/ɪˈræt̬.ɪk/
（动作、行为等）不规则的，不确定的，无计划的
moving or behaving in a way that is not regular, certain, or expected
He drove in an erratic course down the road. 他开车忽左忽右地在路上行驶。
She can be very erratic; one day she is friendly and the next she'll hardly speak to you. 她喜怒无常，今天待你很友好，明天又懒得理你。