For most ToS rules where there is a clear black and white, clear-cut difference between what's allowed and what isn't, the answer is simple. Don't break the rules!

For social rules, I've always imagined they apply when people are annoyed or offended. Cursing in a friendly manner toward another person who is also cursing is kind of harmless. There's a big difference between that and telling an under-performing party member to "**** off".