As the subject says, haven't seen this for a long time but it was once on this board, the title was something similar to "The greatest fight I never saw".
From memory it was between a wife and her sister after someone (possibly their mother) had died and wasn't there to stop them fighting. It's told from the perspective of the husband who can only listen to the fight from outside the room and he describes what he can hear and guess what they are doing to each other. The sister wins and emerges from the room pretty beat up and she blows him. We never see the wife who remains in the room.
Hopefully this is ringing a bell for someone?