It shouldn't be a word ...
Don't tell me about it, Jacki. Tell the Oxford Dictionary - and Merriam-Webster, Collins, Macquarie, American Heritage, Dictionary.com, etc.
Writers have found
unmeant to be a useful word at times. An example from the Melbourne
Age a few years ago was in a review by Barry Dickins of the 2008 film
Australia: "Each scene possesses its secret gaucheness and unmeant hilarity."
But you may have a point about it not being common. I'll consider that in due course.