口是心非-------speak with one's tongue in one's cheek

例句：
A: I don't know why Jack promised to back me up, but he broke his promise.
我不知道为何杰克答应支持我，却失信了。
B: Don't you know he often speak with his tongue in his cheek?
难道你不知道他经常口是心非吗？

同义词：

1.play a double game

2.say one thing and mean another