From blasphemy:
2: "irreverence toward something considered sacred or inviolable"
I'm using that second definition.
Perhaps blasphemy is more general but I have always thought blasphemy was when a person of a particular faith criticized the beliefs of his or her own faith. For example, I do not consider myself guilty of blasphemy when I question the existence of Allah or Krishna. Nor do I consider people not of my faith ridiculing what is sacred in my faith blasphemous because they never believed it was sacred in the first place. Uncouth, ignorant, or deluded, maybe, but not blasphemous.