If you say no right away you look like an uncooperative stubborn mule.
But if you say sure we can look into that and let the bad idea show it’s weakness for you then you can say ‘that was a stupid idea‘ in a softer way without picking their egos.
“Hmm we might be caught for time getting to the airport if we do that”
Or
“I think the focus might be drawn away from the important text and towards the giant purple cartoon pig. Maybe if we reduce it a little bit?”
Thomas Duggan 