As an aside, I find it funny how the English language shies away from calling vulgar words what they are in absolute terms, but instead uses a relative term "inappropriate" without answering the question "inappropriate for what?". That gives me the paternalistic vibes of "for you".
Similarly, "explicit" art is all around, but only vulgar is marked as "explicit".
That's why it's a suggestion and not a feature that blocks you from writing whatever you please. It's like how I can type my last name into documents on computers I have never used before: the spellcheck indicator will show up and I will choose to just ignore it.
Uh, I'm going to be bold and assume the tool is just not made for vulgar tirades. Just how spell checking will bother you if you quote something that's not grammatically correct. /shrug
Oh wait, not in English.
But at least respected dictionaries exist for grammar, offering a vague consensus. But is there a dictionary for "absolute inappropriateness", against which we can check google's checker?