[Pengwin]

This is my approach with things too. Instead of saying know I explain the complexities of what would happen by saying yes:

- Other projects will be pushed out of the way

- Your deadline is not feasible, I can do it by this date.

- The cost/time of me doing something would be high, due to my inexperience in doing that task.

- I personally think it is a bad idea and a waste of everyone's time, but it's your call.

Things may work differently for others, but turning a "no" to a "yes, on my terms" is what has worked well in any situation I've been in.