Room and Broad (1968)

Jerry and Susan are newlyweds, but things aren't going well for them. He's unemployed and a sullen, abusive jackass. She has a job, but is subjected to constant sexual harassment by her scummy boss. One day Harriet, an old acquaintance of Susan's, shows up at their doorstep. Susan seems glad to see her, but what she doesn't know is that Harriet harbors a deep grudge against Susan for something that happened years before, and is plotting her revenge.