Was it the Brushing, maybe?

I asked myself the same questions Ronda, my first follower (Yay by the way :D) asked. What exactly had changed? Or was it a desaster long in the making?
Now, taking a good look at the situation I think it's fair to say that their relationship has deteriorated in the last few years. There have been issues of jealousy, fighting over territory and food, and competing for attention. Flecki was getting smacked around quite a bit in the process as she's smaller, more "sane", and younger.

I myself may have triggered this whole catastrophe. The evening proceeding the meltdown, I gave Idi a brushing. I usually never do this as Idi hates being brushed and Flecki, who loves it, gets soo jealous. Flecki feels that the brush is hers and hers only. So when she heard the familiar sound of the bristles rubbing against my thumb, she got super-excited as I've been so busy lately and haven't had a chance to treat her that way in a while.
How upset she must have been when she saw that it was Idi's turn!! She who doesn't even get it? She who was kind of trying to get away from it all. So I locked Idi in my room and tried it again as I was convinced that every feline simply must love being brushed.
That's when the fighting at the door began. They always stick their little paws underneath the crack and try to whack each other. This time it was accompanied by some serious growling and - oh my - even hissing!! :-o They were both extremely upset at what was going down.
I finally got it. Idi really, really doesn't like being brushed and Flecki wants some. So I did the right thing at last, gave Flecki a good brushing and left Idi alone.

The next day Idi started harassing Flecki in this unacceptable way. I think they both held a grudge against each other. I was just checking out some YouTube videos to demonstrate how bad it was. But there were really no two felines getting at it the way these two did. Most of them were kind of equally matched so it was a somewhat fair competition. Not here at my house. The closest resemblance is the following, I guess. Even though one's a snake. Especially the scene where the snake is throwing the kitty up in the air.  Just picture her being one ferocious feline. Flecki clearly did not win, though. And nobody was as calm as red cat or Jackie at the end of the match here at my place.