Damn I have missed my chance...

According this report,

Telling your boss what you really think of them is good for your health -- and helps managers improve, according to research published on Wednesday.

Firms should be even be encouraged to let employees regularly rate their line managers, to produce "happy, healthy, stress-free employees," said the study presented at a conference of the British Psychological Society.

[...]

"When managers received feedback from their staff, they were more likely to change their management style and subsequently be seen as more effective line managers," said the study.