a slap in the face 打脸

“打脸”，网络用语，字面意思是“a slap in the face”，通常指自己说了某句话或扬言做某件事后却没有履行（fall down on one’s promise），也可以指某人自信满满的断定事态发展，结果却出现与其预想完全（the complete opposite of one's expectation）相反或差距非常大，如一巴掌打在脸上，十分尴尬。

我以为她会答应, 结果她拒绝了我。真是打脸！

I thought she would say yes, but she turned me down. It was a real slap in the face.