There's no such thing as work-life balance for poor Nayul, thanks to her evil boss, Sijin. Not only does he make her work overtime constantly, but she's also dumped by her boyfriend because of it. Fed up with Sijin's demonic ways, Nayul storms to his office to complain... and finds him jerking off! Though the sight is initially grotesque, Nayul finds herself oddly turned on. Somehow, she ends up banging her boss on his desk, which leads to an irritating yet steamy colleagues-with-benefits relationship. But how long can Nayul keep this shameful secret from her prying ex and gossipy coworkers? (Tappytoon)

Original Novel
Original Webtoon

Official Translations:
R19: English, French, German, Thai, T.Chinese, Spanish
R15: English, Japanese

Note: The first korean cover has the official english title as <I Say Please Be Quiet and Take Off Your "Something"> before getting a new cover and title change to <Be Quiet and Don't Ever Smile in the Office>. {Sources; (1), (2)}