面従腹背
men.juu.fuku.hai

Literally: face/mask – obey – belly – back/defy

Alternately: Putting on a show of obeying or going along with someone while secretly opposing or resisting them, at least mentally. This defiance will likely manifest eventually, but as long as it exists within one’s heart, this compound is applicable.

Notes: While most learners of Japanese think of 背 as one’s physical back, and may therefore be amused or stymied by 腹背‘s literal interpretation as “belly-back,” all that’s going on here is being disobedient (背く) in one’s belly (where emotions happen, you know – see also 腹が立つ, hara ga tatsu. “to get angry”).

Literalism strikes again! From this random blog post.