tongue in cheek idiom (also with your tongue in your cheek)
开玩笑地;说着玩地
If you say something tongue in cheek, you intend it to be understood as a joke, although you might appear to be serious.
He said that he was a huge fan of the president, although I suspect it was tongue in cheek. 他说自己对总统极为仰慕，而我认为他是在开玩笑。