Do you think the word concupiscence sounds negative, positive, or just neutral?

It is neutral. Words for possibly sensitive/taboo natural functions e.g. sexuality, going to the toilet etc, which are derived from Latin, tend to be neutral/polite.

E.g. ****, fanny (rude, coarse) pudenda (polite, neutral).

Yea, technically Con. However it has a negative rep

Only for prude Americans.

Concupiscence is strong sexual desire. To see it as inherently negative is to believe that "sex is dirty". Many Protestant denominations tend to see concupiscence as sin itself, an act of the sinner. The Catholic Church teaches that while it may lead to sinful acts, concupiscence is not sin itself. Indeed, the word itself as a distinct term is more likely to be used by Catholics.

The Catholic Catechism defines concupiscence as "the movement of the sensitive appetite contrary to the operation of the human reason" (CCC 2515). St. Augustine wrote a lot about it, was the theological innovator.

You mean like me and doughnuts and cream cakes?

To a great extent it depends on how the word is used in a sentence. But, generally, I agree that it is neutral.