What acts are considered sacreligious/prohibited by christianity?

Answer 1

Sacrilege is an offense against the first commandment.

Sacrilege consists in profaning or treating unworthily anything that has been consecrated to God, including the sacraments and other liturgical actions, persons, things, and places.

Sacrilege committed against the Eucharist is considered especially grave.

With love in Christ.

Answer 2

anything putting down any religious figure or the bible, but every "sin" is forgivable in the eyes of god, no matter how terrible it may be.