This was more weird than outright offensive, but it kinda rubbed me the wrong way...
I was part of a fandom and wrote a very heavily AU piece for it. It was multi chapter and getting pretty long, and gaining a decent amount of positive feedback, when... I hit a wall. I stopped writing the fic, and in the meantime, lost interest in the fandom. Eventually, I admitted defeat, apologised to my subscribers and declared the fic abandoned.
A short while later, another writer contacted me over the IM - to ask if she could have my story! She wanted me to send her copies of the chapter files so she could upload them under her own pen name and finish the story as she so wished!
I'd never heard of such a thing happening, and was surprised at the strangeness and audacity of the request. I think I wrote a quick message about how although I had given up on the fic, I still had an idea of how I wanted it to end and thus couldn't hand over creative control in such a way, but she was welcome to take the basic concept and write her own version of it.