It's a good question.
I think our colleague here would probably have a better idea. I think it is a very rare case that there are requests that shouldn't be acted on. It should be a very, very rare thing.
My concern with a term that subjective and broad is that it could be so easily used by governments. It's vexatious to whom? I do worry that, as it stands now, it could very easily be used by governments to not release information.