Swear words don't break the HN guidelines. When we ask for civility we have in mind how people treat one another online. Swear words can be used to treat others badly, but they have plenty of other uses.
It's not a trivial question, though, and people aren't wrong to disagree. Cultural differences make for very different views here. In some (sub-)cultures swear words are uncivil and in others they are innocuous. There's no model that satisfies all these norms, so inevitably we have to disappoint some.
As a consequence of the above, we don't bowdlerize titles either.