What would you tell your Boss ?

I would try to tactfully discourage him from taking that path. If he insisted then I would keep my mouth shut and let the pieces fall where where they may land for better or for worse.

Oh yes! I have definitely came across this scenario a lot of times. Every boss has their pride and it is best to take your boss's personality into consideration before tackling an issue like this. What I would usually say is this, "That sounds like a great idea and I'm sure it will turn out well! Let's discuss more on the details, who knows, we can actually make it better!" I find that this works with alot of bosses. Not only are you telling him that you find his/her idea great, but you are also showing him/her that you are very interested in it. So then your boss, seeing that you are interested will share with you his/her ideas. And then he/she would expect you to share back. And that is when you can subtle drop hints on why you think his/her ideas stinks. I have tried this on a few bosses, sometimes we will come up with better ideas and some of them even admit that their idea did suck. When they do admit, I'll say "Hey, no idea is a bad idea...at least you brought it up" Yeah...so that is how i handle the situation...