Racist “jokes” make people uncomfortable because it’s directly adjacent to racist insults, racist hiring/firing practices, and even racist violence. Employers have a duty to workers from employees that are potential threats, and to remove employees that are walking legal liabilities. And that very much includes employees who claim to be “equal-opportunity offenders.”

I understand that it’s more complicated when you are making jokes about your own ethnic group. But please understand that it’s not an issue of “bad culture fit.” As an example, employees who make relentless personal criticisms of their coworkers aren’t gruff people that have trouble fitting in to an upright corporate culture: they are jerks whose behavior rightfully makes them difficult to work with and hard to justify hiring. It is the same with making ethnic / racist jokes in the office. Just don’t do it.

(There is also a difference between ethnic jokes about Poles and racist jokes about black people or Jews, but that’s a different discussion. Both are really not appropriate for the office.)