...Well, yes, I have read it before, and in all likelihood, you have too. I say this with some confidence, because you won't just find it in literary critiques, but in Little Women, David Copperfield, and Our Mutual Friend. Here's the Little Women quote:
A restless movement from Laurie suggested that his chair was not easy, or that he did not like the plan, and made the old man add hastily, "I don't mean to be a marplot or a burden."
And here's the one from David Copperfield:
Which you haven't, you Marplot,' observed my aunt, in an indignant whisper.
So what is a marplot? According to the Free Dictionary, it is
A person who spoils a plot or who ruins the success of an undertaking or process.
But where does it come from?. Well, actually, this is quite interesting. It comes from a play called The Busy Bodie, written my one Susannah Centlivre, a woman playwright born sometime around 1669 and dying in December of 1723. She is noted as the most successful woman playwright of the 18th century, and the woman second only to Aphra Behn as a woman playwright of the English stage. If it got to Louisa May Alcott, you know The Busy Bodie must have traveled. And in fact it has traveled all the way to the 21st century, as this blogpost gives witness to.
You don't have to rely on The Bent Quill Players or for that matter me to give the thing life. You can just head on over to Project Gutenberg and read the text of The Busy Bodie your own self.