Category term for "polite", and "offensive"

Solution 1:

I'm not aware of any word that's a good fit in the sentence as shown; more possibilities may exist if agnostic is replaced by neutral or free. However, consider the word value:

It's not specifically polite, but it's not offensive either; it's value-agnostic.

Note, value is being used above to represent rules, principles, conventions and judgement regarding manners, etiquette, civility, politesse, habits and behavior, rather than in some other sense.

Two possible rewordings that avoid the need for a word as requested include the following:

It's neither specifically polite, nor offensive either; it's neutral.
It's not specifically polite, nor offensive; it is amoral.

Solution 2:

How about mores:

A set of moral norms or customs derived from generally accepted practices. Mores derive from the established practices of a society rather than its written laws.

So you'd have: "It's not specifically polite, but it's not offensive either; it's mores-agnostic."