be laughing on the other side of your face idiom UK (US laugh out of the other side of your mouth)
到时候就笑不出来了，得意变失意
used to tell someone that, despite being pleased now, they will not be pleased later when things do not happen as expected or planned
She's pleased with her promotion but she'll be laughing on the other side of her face when she sees the extra work. 她很高兴自己能获得晋升，不过等她明白自己要多干不少工作时恐怕就笑不出来了。