Given how long ago the term “nivul peh” was first used, it should
be obvious that it doesn’t refer to specific modern words.
It definitely refers to pritzus – see Mesilas Yeshorim chapter 11.
The use of non-pritzusdik but vulgar language would fall under the
concept of lashon n’kiyah. I don’t know of a requirement not to
hear other people be vulgar, although presumably one’s nature
ought to be refined enough that one would want to avoid doing so.