play fast and loose 反复无常；朝三暮四；轻率对待

【例句】
That guy has a bad reputation of play fast and loose with the girls around him.
那家伙名声很坏，对待他周围的女孩们朝三暮四。

He always plays fast and loose with his commitments, making it hard to trust him.
他总是轻率对待他的承诺，让人难以信任他。