SOLVED Family Gathering Dark Comedy
There is this dark comedy set around a family gathering, maybe thanksgiving or christmas, from recent years IIRC.
This middle aged guy with "flexible morals" comes to the family gathering with intention to hook up with his sexy niece. When he is close to getting her he decided against it. Later he discovered the niece is having an affair with another in law. He bluffed about having recorded their affair to trick the in law to confrontation/confess.