ok so in this case I would probably expect them to say:
the requirements are unclear - that right there is them having an idea how they are going to be able to give you an estimate, by forcing you to be clear in your requirements. That would actually be an engineer being honest.
or
there is a history of changing up requirements on issues like this, I can give you the estimate of what it will be with the current requirements but if the requirements change, as in my experience they are likely to, then that estimate will have to change as well. - this would also be an engineer being honest.
Both of those honest examples aside if the engineer replies no I can't make an estimate and I never will be able to it is probably the engineer being a bit pissy. And I know definitely one or two guys who would exactly behave in this manner.
unless you are dealing with the first time implementation of something that there is only mathematical theory backing it and no previous implementations in the world, I have a hard time seeing how you can construct a situation in which an engineer cannot come with an estimate AND cannot find a way to figure out what they need to come with an estimate (more specific requirements, research on the matter). If they can't figure out at least one of those things I'm going to think it is probably a limitation on the part of that engineer.
Finally, I am an engineer. Although I tend to be one of those arrogant guestimaters, which is a failing in my personality.