逢场作戏 féngchǎng-zuòxì

[play;pillow fight;join in the fun on occasion;act according to circumstances;take part in merely accidental amusement] 原指卖艺人遇到合适的演出场地,就开场表演。后用作随俗应酬,凑热闹的意思

借君拍板与门槌,我也逢场作戏莫相疑。——宋· 苏轼《南柯子》