[steventhedev]

In the case of a truly bad idea, it is the duty of the CTO/VP Eng/Team lead to give the employee the time to explore the idea/discuss it and realize why it's a bad idea. The employee should grow as a result of the experience, and become more valuable in the future.

On the off chance they don't learn, and the situation repeats itself, it may be prudent to refuse such requests.

That having been said, the worst situation is when the boss agrees that it needs to get done, but can't find where to sneak it into the schedule. It's effectively saying that you don't value the happiness of your employees and can't schedule/push hard enough.