Given that the game doesn't give you the option to customize your in-game name, it isn't on the publisher nor developer. Report their Steam Profile via the Report Button and let Valve deal with it if it bothers you.
Steam Community Moderator for Insurgency Sandstorm, World War 3, PAYDAY 2, Battalion 1944, Black Squad, John Wick, Raid World War II, and Overkill's The Walking Dead. Past Experience: Warner Bros, Activision & Skydance Interactive.
As a couple of people have said, as we use Steam names, these are their Steam profile names. If you see a name that is racist, sexist or otherwise awful like this, please report it to Valve using the Steam Profile Report functions.