As a state university, the institution would be subject to First Amendment restrictions on their restrictions. They cannot prohibit expression of religious or irreligious viewpoints, they cannot prohibit expression of racist or anti-racist viewpoints, and so on. That said, there may be some murk pertaining to anti-discrimination legislation and the concept of a hostile environment. See for example this statement from U. Michigan: the underpinnings of any such restrictions are pretty broad (see the USC statement, including titles VI and VII of theCivil Rights Act of 1964, Title IX of the Education Amendments of 1972, and so on – those sorts of concerns apply to private schools as well).
SWOSU has a long list of prohibited activities. The only rule that marginally looks like it could cover bad language is the ban on
General misconduct that adversely affects the student's suitability as
a member of the university community such as immorality, commission of
major crimes, inciting disorders, association with known criminals,
peace disturbances, disorderly conduct, and all acts that recklessly
endanger the students or others.
And that would be an incredible stretch.
The residence handbook states, pertaining to the rooms, that
Obscene material, including, but not limited to, pornographic
literature, X-rated movies, and displays of profanity or language that
is offensive to others may not be displayed.
I assume that someone would be offended by the B word, so you can't display that on a poster in your room. This does not apply to verbal profanity or profanity in the lobby. Since they don't make the residency agreement publicly accessible, I can't see what they might have said there that implies a no-profanity rule. I should mention that university employees often over-interpret their authority, so it is not guaranteed that this is actual university policy (even is distributed by the front desk in a dorm). It may, however, be necessary to sue the university in order to get a clear indication that this is official policy, and that the policy is not a violation of the First Amendment. I would expect that the rationale has to do with "hostile environment". A second runner-up would be that it's about "disorderly conduct", which is where Florida A&M places their anti-profanity rule.