Do we really have to call out "don't cuss"—it sounds like a schoolhouse rule for a bunch of kids that don't really understand what being civil means. On the whole lowers whatever code from a positive ensemble designed to promote elevated dialogue into some checkmark set of rules where I feel I could whine "BUT I FOLLOWED EVERYTHING, Y U BAN?!"
Rather than admonishing us salty swine, I'd rather see something like (please note that I am not a wordsmith and you should not use the following)
Choose your words carefully. Stack Exchange (or $SiteName, what is this, PHP?) is used at work and home, by people across the globe. Think before posting an inflammatory remark, even as a joke. Be appropriate and maintain a level of professionalism...yadda yadda.
For those that choose to interpret such a statement as "I do what I want", in practice things would remain basically the same. The warning could explicitly direct them to the policy post that swearing is strongly discouraged, and excessive use (presumably they've used some already) may carry with it consequences.