accidentally on purpose idiom
明明故意却装出无心的样子；假装不是故意地
If you do something accidentally on purpose, you do it intentionally but pretend it happened by chance.
I've never liked these glasses of Peter's. I might drop them one day - accidentally on purpose. 我从来就不喜欢彼得的这副眼镜，或许什么时候我会假装无意把它给摔了。