What would you say to your boss if he is crazy about an idea, but you think it stinks?

No idea is bad. If boss thinks it's crazy and wants to do it then so be it however I'll give him my perception of stinker thought ina very polite manner and probably make him to rethink his idea.

I would clearly say him that I was not fine with his idea when I have already known his idea's impact would be unfair and I would ask him what if something goes wrong when his idea is being implemented.

As an Engineer I would try to give a logical explanation mostly in mathematical way. If he withstand with his decision then I am with boss, support the company as team member and do my job whatever is given to me and try to put my best.

Before approaching the Boss, I will analyse the problem related to that idea and try to solve the problem. If don't then I'm going to share the drawback problem related to that idea with the Boss. So, that Boss can rethink and try to solve the problem.

I'm trying to put all my interest in the idea that asset together with a solution for this idea.

Yh. Its my duty to follow all the orders of my boss that are related to job but beside this its also my duty to work for the benefit of company only they recruited me so that I can share my thoughts and ideas to them, first I try to analyse difference between mine and my boss thoughts and still if I think myself better in thoughts then I directly asked my boss to share my thoughts on that particular project.

Each and everything have its own time to express. As mentioned, your boss is crazy about the idea, you should leave him with his state of mind for at least 10 to 15 minutes. After that surely every boss will ask for the employee opinion, time for you to express it with a proper evidence.

Sir, I will say. I'll completely agree with you and ask him some time to come up with some suggestions for improvement after discussing with all employees. And ill come up with some changes to it to make it great decision. Telling to him, sir these little changes can make your incredible idea to exquisite idea.

As I am a fresher, my way of thinking may clash with his, I try to suggest any better alternatives or improvements in a subtle way.

Firstly, the boss is never always correct and If he has a great idea, one should never correct him or suggest that it is of substandard quality on his part. The best approach should be initially to request why and how he has come to the idea and why he favors it to be implemented.

Only then can you, yourself, have the ability to understand whether you can provide alternative options or counter-arguments. If it is truly a bad idea, this approach will surface the disadvantages and at the same time keep yours/his integrity and relationship intact. If at that time you have alternative suggestions to perhaps complement his idea, then this would be the right time to make them.