You don't know what it means to blaspheme God, Ugly - and, no, calling It a donkey-raping shit eater, while disrespectful, would not be blasphemy.
Claiming god is not real is not blasphemy.
Calling believers morons is not blasphemy.
I could write a whole fucking tract on what blasphemy is, but I'll keep it short:
It's made clear over and over - there's no killing on God's holy mountain (Isaiah 11:9 among others)...what you do to even the humblest persons you do also to God (Matthew 25:40 among others).
(This applies also to animals. Oh yes, there was animal sacrifice because the ancients believed it was necessary, but pointless cruelty was banned pretty much outright: One of the most ancient Abrahamic laws - which fits with allowing the oxen to tread corn unmuzzled or lightening the burden of an enemy's donkey - is the prohibition against eating animals alive - Genesis 9:4.)
Cruelty by one creature against another is blasphemy. And people, both religious and non-religious, commit the most egregious and blasphemous of acts every day.
I speak the truth in this. Atheists and theists alike can and should test my words by the fruit they bear.
@ Thinking Allowed: The Bible speaks of, but never defines, the 'unpardonable sin' not as blasphemy against God or Jesus (or presumably the prophets) but rather as a very specific - and, again, unnamed - act of blasphemy specifically against the Holy Spirit.
Warning: What some people consider to be religious bullshit ahead.
Within each person, close readers and students of the Bible will read, there exists a Naós (Strong's 3485); the Holy of Holies where the Ruach of each dwells alongside the Spirit of Life. If there is truly an unforgivable sin, I believe a person would have to deliberately carry it out whilst believing fully that the act is both a sin and unforgivable. I don't know that such a person exists anywhere in the world, and for that I am truly grateful.