疯子也有疯子的疯度
[fēng zi yĕ yŏu fēng zi de fēng dù]
A Lunatic Has a Lunatic's Degree of Madness implies even crazy people have a limit to their madness. It suggests everyone, including the 'crazy' ones, has standards or levels they will not go beyond, no matter how unconventional their actions seem to others.