I can't believe I just noticed this, and maybe someone else has noted this already. But Damien has a habit of wringing his hands around his cane when he's stressed.
Dark does something similar: he pulls at his lapels when he's stressed/pissed/scared. You see this a lot in "Darkiplier vs Antisepticeye" when things start to unravel and even at the very end with Dark!Chica (although it's cut off at the bottom).
Always the hands in fists, always the tension over a lack of control over the situation. Perhaps Dark does this because he doesn't have anything to fidget with anymore.
This man has been so goddamn stressed for over a century, let him REST.
As much as I love the "Anti and Dark fucking hate eachother, it's hands on sight as soon as they're in the vicinity of each other" I wanna propose a new version of their dynamic that I don't see very often.
This is going off of the idea that Anti is an eldritch being possessing the body of a human (c!Jack) in order to exist in this reality. It's a bit more complex than that but the summary is Anti is completely detached from Humanity.
Now imagine that from Dark's perspective. They might not be human anymore but they do know what it means to be human and I do think there's a part of them that grieves their loss of humanity. Especially since Dark never asked for this existence, it was something they were forced into.
Dark knows what it's like to be human which is something that can't be said about Anti.
If Dark is a soul so broken and shattered that it can barely resemble a human soul any more, then Anti is the complete lack of a soul and it doesn't grieve that.
I could fully imagine Dark assuming that Anti is like them in some way, another shattered soul that's consumed with the emotions and mental turmoil of what happened to them- they might've even found comfort in the idea of someone else being like them in this pain.
Only to realise that Anti is nothing like them. Anti has no remorse or grief or turmoil, it never has and never will care about any human or anything that comes close to one. It puts a whole new perspective on Anti calling Dark "weak" and comparing them to c!Jack. All humans are the same to Anti- weak.
THIS is why Dark hates Anti in my opinion- because Anti is just as cruel and careless as the person who forced them into this role. Anti equally hates Dark for them masking around as something that Anti thinks their not- Anti still views them as being human, a human pretending they're something greater than what they are- and Anti, who genuinely does see itself as being above humanity, despises that with every ounce of its being.
Something I’m pretty sure I’ve said before but no one else talks about is in Darkiplier vs Antisepticeye Dark just goes so hard on Anti for no reason and Anti has zero reaction to it
Dark basically says “why don’t you go kill yourself again?” and Anti’s response is basically “why don’t you go put on more makeup”
Dark my man I love you but you did not need to go that far and Anti what the fuck was that response