Gumapang Ka sa Lusak (English: You Crawl in the Mud), also known internationally as Dirty Affair, is a 1990 Filipino crime drama-action thriller film written by Ricky Lee and directed by Lino Brocka, both of them are National Artists. It stars Dina Bonnevie, Eddie Garcia, Charo Santos, Christopher de Leon, and Allan Paule.

Produced and distributed by Viva Films, the film tackles the abuse of power and evil acts committed by Edmundo Guatlo in which Rachel, a movie actress who is his mistress, and her friends try to expose his scandals and violent acts done by him and his henchmen to the public.In 2010, the film was remade into a television drama series of the same name by GMA Network as the nineteenth installment of Sine Novela and starred Dennis Trillo as Levi, Jennylyn Mercado as Rachel, Al Tantay as Edmundo Guatlo, and Sandy Andolong as Rowena Guatlo.