This trope is when a character has relations with his boss's lover. If a man in an office setting ain't sleeping with the Sexy Secretary, then he's probably sleeping with the Boss's Wife. Contrary to Sleeping with the Boss him/herself, which is usually performed by those intent on Sleeping Their Way to the Top, an underling betrays his boss's trust with infidelity. Sometimes, it is brought upon by the guy hating his boss and doing it out of spite, or being seduced by the Femme Fatale wife.
In most cases, it ends with a fatal love triangle between the three, either resulting in the boss's or the employee's death (sometimes, albeit more rarely, the wife's). If the underling is lucky, he will merely be Reassigned to Antarctica or fired, but if the boss is an outright villain, expect a prompt serving of You Have Failed Me if he finds out. If the boss is not quite so overt, an Uriah Gambit is also likely. However, if the boss ends up meeting an unfortunate end, the underling instead might take his job position along with his wife.
- Blacksad: Hans Karup's wife Jezebel is having an affair with Huk, his second-in-command in the Arctic Nation, the white supremacist cult they're both part of. Huk uses unsubstantiated allegations that Karup is a pedophile to engineer his betrayal and execution by his followers, even whispering that he'll take good care of Jezebel after he's gone. This backfires on Huk, as Jezebel later kills him for becoming too much of a loose cannon in her own years-long scheme against Karup.
- The Punisher: In an early story, a mob boss routinely mistreats his underlings, including killing them. When he and another mook open a door to find an explosive with only a few seconds left, the mook tells the boss he's been with the boss' wife for the past two years.
- Red Ears:
- A one-page gag has an office worker feeling dismotivated with his work, so his boss tries to cheer him up by telling him how great it felt when he had rowdy sex with his wife a week ago, and suggests that his employee do the same thing. The next morning, the employee waltzes into the office full of energy. Only a passing comment about his boss's curtains reveals that he took his advice rather literally.
- Another joke has a guy walking up to a housewife, slowly coaxing her to undress herself for massive sums of money, before convincing her to sleep with him for an even larger sum. She agrees because her husband's business is apparently in dire financial straits. When her husband comes home later, he asks her if anyone came over. When she denies, he curses "that lazy employee of mine" for not delivering the cash money he ordered him to earlier that day.
- Batman (1989): Jack Napier, the Number Two of the Gotham City Mob, is sleeping with his boss Carl Grissom's mistress. Grissom sets him up to be killed for this betrayal, but it doesn't take. After Jack becomes The Joker, he murders Grissom in retaliation, and to illustrate that he's gone completely Ax-Crazy, has the mistress offed as well when he grows bored of her.
- In Blood Simple., Ray sleeps with his boss Marty's wife, Abby, resulting in Ray and Marty's deaths.
- In Buffalo Soldiers, Private Elwood is sleeping with his superior Colonel Berman's German wife behind his back. His boss is enough of a dimwit that he never suspects a thing, and still believes that Elwood is a stand-up soldier after he's forced into early retirement as a result of Elwood's machinations.
- Cliff Garrett from The Hitman is an undercover cop working as a hitman for The Mafia. He has a fling with a mob lawyer who happens to be the boss's squeeze. When the boss finds out, he has Garret sold out to his rivals and the girl killed.
- In The Last King of Scotland, Nicholas Garrigan drunkenly has an affair with one of Idi Amin's wives, Kay, made even worse when she becomes pregnant as a result of the encounter. This ends in Kay being brutally murdered when she tries to get an abortion, and Nicholas to be tortured with meat hooks after he tries to assassinate Amin, with Amin clarifying that he knew about him and Kay all along.
- In Miller's Crossing, Tom sleeps with his boss Leo's girlfriend, Verna, resulting in a heated mob battle among several parties.
- Invoked by Frank Castle in The Punisher (2004), when he stages things to manipulate mob boss Howard Saint into believing that his right-hand man is having an affair with his wife. The minion was actually a closeted gay man, which Howard didn't know, but his wife did. He doesn't believe her when she brings this up, thinking she's tarnishing his friend's memory, and kills them both, only to be horrified when he discovers the truth from Frank later.
- Happens in The Secret of My Success (1987). Vera Pemrose Prescott is the wife of Howard Prescott, the CEO of the Pemrose Corporation. She seduces Brantley Foster, an employee at Pemrose, and has a sexual encounter with him. She only did so because she wanted to get back at her husband for having an affair. Foster himself only finds out that Vera is his boss' wife right after he sleeps with her. He also discovers that she's his aunt, because at that exact same moment she finds out that he's her nephew by marriage.
- Defied in They Drive by Night. Lana Carlsen clearly has a thing for her husband's employee, Joe Fabrini, but Joe never responds to any of her advances. Initially, it's because Joe considers the boss an old friend and would never betray his trust like that—and Lana responds by murdering her husband. Then Lana discovers that Joe already has another girl anyway, so she tries to have him implicated in her husband's murder.
- Of a sort. In the story "Ring of Gyges" from Plato's The Republic, an ancestor of King Gyges of Lydia was a humble shepherd who happened upon a magical ring that gave the wearer invisibility. Taking advantage of this new ability, the shepherd went on to sleep with the Queen, kill the King and take the kingdom as his own.
- In Aubrey-Maturin's first book, Jack Aubrey is sleeping with the Port Captain's wife, which has severe consequences for his career ongoing as said Port Official knows and constantly goes out of his way to deprive him of men, supplies and delay news of his successes to England which probably prevents his promotion
- And Then There Were None: General John MacArthur's reputed crime was sending his wife's lover, who was one of his subordinates during World War 1, on a suicide mission in a ploy to get rid of him. He grows to regret his action years later.
- In Altered Carbon episode "Fallen Angel", Kovacs is seduced by his trillionaire retainer Laurens Bancroft's wife Miriam and Coitus Ensues. This creates tension in his relationship to Bancroft later in the series.
- Californication: Hank Moody has sex with a drop-dead gorgeous black woman after meeting her on a plane ride before discovering that she's the main squeeze of gangster/rapper Samurai Apocalypse, who has hired/forced Hank to write the script for his new movie. This becomes a massive worry for Hank, who rightly fears that SA—who isn't averse to a High-Altitude Interrogation—will kill him, which he almost does when he finally finds out (Hank survives with a flesh wound).
- Dexter: When Lieutenant LaGuerta is demoted and replaced as head of the Homicide division by Lt. Pascal, she Gaslights Pascal by striking up an affair with her fiancé, all while playing the Graceful Loser in the office. Pascal's anxiety over her deteriorating relationship causes her to behave erratically at work, which gets her removed and lets LaGuerta reclaim her position.
- This forms a major subplot in season 4 of The Sopranos, when there is massive Unresolved Sexual Tension between Tony's underling Furio and Tony's wife Carmella. They never consummate it, but Furio does consider murdering Tony before skipping the country and going back to Italy. When Tony finds out, he has a contract put out on him.
- In the second season of Boardwalk Empire, Owen Slater sleeps with Nucky's mistress Margaret, though they don't start an outright affair until midway through season 3, once Margaret's marriage to Nucky has fallen apart. It ends when Owen is killed trying to whack Joe Masseria as revenge for Gyp Rosetti's attack on Babette's, and his body is shipped back to Nucky in a box. Nucky only learns of the affair when he notices the reaction Margaret has to seeing Owen's body.
- In the Masterpiece Theatre Mini Series Reckless a doctor falls in love with the wife of the chief of staff and resolves to make her his.
- Defied by Joseph in The Bible, more specifically, in the Book of Genesis, when Joseph is a slave of Potiphar's. Potiphar's wife tries to seduce him, but he resists, both out of loyalty to his otherwise benevolent master and because infidelity is a big no-no under both Jewish and Egyptian law. However, out of spite Potiphar's wife accuses him of having raped her and Joseph finds himself wrongfully imprisoned.
- Also from The Bible: in 2nd Samuel, Abner son of Ner is accused by King Saul's son Ishbosheth of sleeping with his father's concubine, which makes Abner so upset over the accusation that he decides that he would no longer support Ishbosheth and instead hand over the rest of the nation of Israel to David to reign as king over.
- In most versions of the King Arthur mythos, the downfall of the Round Table is heralded by Arthur's friend and subordinate, Lancelot, having an affair with Arthur's wife, Queen Guinevere.
- Eric from The Human Pet was revealed to have done this through a series of vlogs his captor, The Codemaster, found on his computer and shared with YouTube. Who initiated it and what happened after the affair is unclear, but what is clear is that it ended with a death and it is why The Codemaster is targeting Eric.