act up 〈口〉 1. (机器)运转不正常；(疾病)发作 The vacuum cleaner is acting up again. 真空吸尘器又出毛病了。 His stomach had been acting up constantly. 他的胃病经常发作。 2. 耍脾气；捣蛋 The boy acted up whenever guests came. 这男孩一有客来就发“人来疯”。 Act up and I'll beat your ass. 你敢捣蛋，我就打你个屁滚尿流。 The river frequently acts up. 那条河常闹灾。 3. 代行更高的职务；晋升