Last summer, I had a temporary job which lasted 3 months (not more, not less) as a research engineer.
It was decided that if my work gave promising results, my superior would write an article about it (To be published in research papers). Actually, it would have been nice for me to write the article if I had the time. This was an oral agreement between us: writing an article was not in my goals.
The contract goal was to develop a piece of software, and I did, but I didn't have the time to write the article.
Months after I left the company, my superior contacted me by email and told me to write the article, because there was a big conference coming up and that my work was worthy of publication (hence the demand ages after the end of my mission).
I say he "told me", because he was not asking, he was saying that I needed to write the article and give it to him. I was very upset because he never believed in me by the time I was in the company and repeatedly insinuated that I had no talent. My mission was over, I had no obligation to write this article. If he'd been nice with me, I'd surely have written it, but since he was very unpleasant to me, I had no will to do what he wanted me to.
How could I have tactfully let him know that I didn't have to write this article, since my mission was over and that it was not a goal of mine in the first place? He's been awkward with me the whole time but I'd have liked to tell him in a polite way.