I didn't invent this term. Some other protectors of the 2A did, but I use it, and here's why:
The use of "Dancing in the Blood" to describe the immediate, almost instantaneous, use of the horror-effect (blood) of any gun tragedy to bash guns and not perpetrators is a cold, calculated plan for the gun-bashers. In the three latest mass killings, the first public statements calling for strict gun control happened well before any police investigations had finished, well before the motives of any perpetrator were known and even before it was known how the perpetrators had acquired their firearms.
What was obvious about the gun-ban proponents in each of these tragedies was that they sought to make their initial push to use the events to further their cause at the height of public revulsion at the first news of the crimes. Had they been able to actually go to the crime scenes and come before the cameras carrying out dead, bloody children, I have no doubt that they would have done THAT, as well.
Now, the other side of the coin. It is a complete, stark lie to claim that defenders of the Second Amendment also "Dance in the Blood" after these tragedies. The defenders of the Second Amendment run purely defensive campaigns when these events occur. Yes, immediately upon hearing of the tragedies, I go on watch for what has become the inevitable "Dancing in the Blood" of the gun-banners. Yes, immediately upon hearing the first "Dancing in the Blood" statement, I fire right back. When the pirate ship sails into view, is it wrong to roll out YOUR guns before they've fired their opening broadside? Not really, you're just preparing for what appears to be an inevitable battle. We defend the Second Amendment and the Civil Right it enumerates, that's all. What kind of a warped mind can say that a purely defensive stance is somehow the same as the offensive (in both senses of the word) tactics of the gun-banners?
I'll stop calling a spade a spade when it looks like a diamond, heart or club, not before.