Let's review:

What Is Blasphemy?

Blasphemy is speech, writing, or behavior that shows contempt, disrespect, or severe irreverence toward a deity, sacred objects, or something considered holy.*

It can take the form of direct insults, mocking religious figures, or treating sacred things with casual disregard.*

Religious Contexts

Christianity:

The Gospels record a unique, permanent offense known as blasphemy against the Holy Spirit, or the "unforgivable sin" (Matthew 12:31-32, Mark 3:29, Luke 12:10).*

Christianity views blasphemy as a serious sin of the heart and tongue. The New Testament uniquely highlights "blasphemy against the Holy Spirit"—attributed to willfully calling divine works demonic—as an unforgivable sin.*

A Hardened, Final Impenitence: Reaching a state of spiritual deadness in which a person permanently rejects the Holy Spirit's conviction, has zero desire for God, and refuses ever to repent.*

Desecration of the temple of the Holy Spirit is also blasphemy. Disrespecting and dishonoring the body, desecrating the temple of the Holy Spirit (1 Corinthians 6:19-20), causing impure thoughts, hearts, and bodies, and blocking and rejecting the Holy Spirit through violations and harm are extremely blasphemous.

Note: 

The greater the blasphemy, the greater the unforgivable sin, the greater the damnation, and the greater the living agonies—agonies experienced when in contact with holy activations due to extreme unholiness.

Note 2:

Though some Christians believe that God is all-forgiving, they neglect that any kind of disrespect against the Holy Spirit, however slight in the mind of the offender, can be punishable by death, as experienced by Ananias and Sapphira, who were struck down dead for lying to the Holy Spirit (Acts 5).

*Referenced from Google AI search: What is blasphemy?