What, precisely, in your own words, is 'blasphemy'?

Blashemy is the disrespectful utterance or action concerning god or sacred artifacts, it's an act of cursing or reviling God, it's the crime of assuming to oneself the rights or qualities of God .... and therefore it is a sin!

I was always under the impression it was simply claiming to BE God.

i swear it's not......Hell it's not...

Blasphemy is anything that disagrees with whatever a fundamentalist religious fanatic thinks reality is.

Its not a sin... there aren't any specifics on what you can and can't say. Those who disagree with me will cite the ten commandments, but even the commandment concerning this is very vague. 'Everyone' seems to agree yelling 'Jesus Christ!' in a moment of anger is taking the Lord's name in vain, but what about the more casual 'God only knows' when confronted with a moment of uncertainty? The definition changes depending on who you ask, and when that's the case, really what can you do?

Its a hold-over from the Old Testament primitive, jealous, vengeful, childish, bully God. Take any name you want in vain... Nietzsche said it best: "God is Dead."

what do you think? is it?

Using the name of God in vain..It is a sin.

A word I can say when I want to sound deep and at the same time tell someone their wrong.

Example of my usage online (Which is the only place I use it. In Urban Terror, an First person shooter online game)

Him-"Man the SR8 sucks"
Me-"Stfu before I rape you with a broom"
Him-"No man, it does"
Me-"Blasphemy!"

An offense invented by religions and churches to give them the worldly right to punish those who act against what they deem "will of god". So basically: a big cheat to keep and extend their power.

Blasphemy is a concept invented by religious people to conjure an offence from the words of people who think that they're full of crap.