A romantic (or possibly platonic) relationship between two individuals that is heavily antagonistic- a dynamic laced with far more frequent arguments and verbal altercation than what typically comprises a romantic relationship. Most used in reference when the altercations are over inane matters.
"So what are Alice and Frank arguing about this time?"
"Apparently he ate most of the green M&M's, and I guess those are her favorite..?"
"Sheesh, that's even more petty than yesterday's argument. They're in such a foemance..."
foemance or fomance means an occurrence of romance between two individuals who are enemies to each other.
"That Leon and Ada kiss in the Resident Evil game was good fuel for foemance."
"Why are Potterheads always shipping the idea of a Draco and Hermione fomance?"