Inspired by this
thread, but I didn't want to hijack it.
A man and a woman somehow end up sharing an apartment. One of them is a total slob, and the other extremely fastidious. At first they find each other highly annoying, but eventually their foibles have them falling in lust with each other: each one provides what the other one lacks in their lives.
The obvious approach would be to make the man the slob, but that's way too obvious. So I'd probably make the woman the slob. If I were going to write it, which I'm not, so it's up to you!