I've had Spider, a large, for a year. He's always been very timid despite his size and always ran off so fast when he saw me that he'd fall over. He was a push over with the other crabs - literally. Even the small crabs would roll him out of his burrow and steal it. The only time he ever stood up for himself that I saw was when he had a window at the front of the tank and I put my finger up to it. He charged at my finger, pinchers snapping and hit the glass so hard that there was an audible crack.
He came up from a molt, probably about 3 weeks ago and was still timid until probably a week and a half ago. For the first time, he stopped running away from me, and started seeking out the other crabs to "talk" (tap antennas) with them.
That's when the trouble started. I'm not sure if he's saying something bad in crabby language or if it's the over enthusiastic way he runs over to them like he's going to steam roll over them, but after a few seconds of talking, they usually either turn their back to him or run away from him as fast as they can. The only one who will sit with him is Cinnamon. It was quite sad, because he'd slump and look all lethargic when they ran off or ignored him. I was actually starting to think he may have been a different species or something and couldn't communicate with them.
Today, he ran up to Ghost and tried to talk to him. Ghost was pooping and I do not think he liked the interruption, because he turned his back. Spider bristled and got all stiff legged - something I've noticed the Aussies only do during altercations over shells or when they are about to fight. Then Ghost bumped him and Spider got really aggressive and started hitting him. After some terse antenna tapping, Spider walked off.
Later, Spider cornered Ghost, grabbed his shell and started rolling him over. I separated him and Spider buried himself.
Just now, Cinnamon was walking along the front of the tank, passed a driftwood cave and this white blur launched itself at her. It was Spider. He stopped short of touching her, but he was really jerky, stiff legged and aggressive looking. She didn't see him because he was behind her. He turned, walked away, then turned back and charged at her again. He repeated that about 6 times and then ran off.
I am perturbed. This is highly out of character for him and I'm not at all sure what's going on. I hate isolating them, because it always seems to stress them out rather badly, but I'm not sure what's going on or what to do. He's been so incredibly passive for a whole year and now suddenly he's acting like this. It's like a switch has flipped.
He has plenty of shells, there's only 8 crabs to a 120 gallon and there is always protein available to them.
I don't like having aggressive crabs
Termite is really bossy, but the only time he's ever grabbed another crab was when he grabbed a female and that was when all my males seemed fixated on mating. So, I'm at a loss. The only things I can think of is that he's somehow mad that the other crabs have been walking all over him for a year (his fault - he never ever stood up for himself), that there is something wrong with him, or that he's a different species (we do have a few here) that got collected by accident and can't communicate with the others properly.
he's usually skittish, but is ignoring me completely even when I had my phone a few inches from him for the photo - usually he runs off when someone enters the room. They are barely moving, he only moves if she moves. 
a couple people have mentioned that they had a PP that was just nasty to everyone, but was perfectly happy to have his own place