(I wrote this down at like six in the morning, and I say similar and similarities and stuff like that a lot so forgive the repetition and if the first half doesn't make a lot of sense)
Now, I know it's really obvious that Janus was very much hurt about Roman's making fun of his name and had decided to lash back. That is not what this theory is.
This theory is that, I think Janus has been subtly comparing the twins the whole time. Because there are similarities there, ones that Roman intends to block out as much as possible. Assuming Janus and Remus are a lot closer, it'll be easy to say that Janus knows is actions and how he behaves, which again is obvious.
But, back when DWIT first came out, someone made a joke saying that Janus' reaction to the Pinata comment (37:30 in SvS) was a lot funnier now that we knew Remus, thinking of it like "Deceit assuming Roman was the nice one and not as chaotic like his brother and being very much shown that was incorrect."
And yes, the twins have similarities, more than can really be listed here in specifics, they have both acted similarly, they dress similarly, and have said similar or even the exact same thing.
Roman wants to deny that he has anything to do with Remus, that they aren't similar at all, he knows that isn't true but it helps keep his black and white view of the world in tact.
What does this have to do with Janus?
Well, I'm merely speculating, but I think that Remus had said the exact same thing about Janus' name when he first heard it. Because of their similarities.
Also because Janus didn't seem all too surprised when Roman said that. He was surprised Roman laughed yes, but after Roman actually said the insult he was just mad. Janus knows that Roman and Remus are similar and with how Roman had been acting not even minutes before towards him.
He just snapped.
I don't think Janus was trying to give Roman a mental breakdown intentionally, I think he was more just upset that Roman kept going on about good and evil and how Deceit is bad and such, when he acts a lot like his brother sometimes.
I have another theory I need to write down on this but Roman kind of needed the wake-up call, that the world is not black and white. And you know what? That's okay.
Janus did go a little far let me say that, but Roman kinda had it coming.
Anyways, that's really all I have for this theory! Thanks for reading! Let me know what you think!
(I'm watching Game Theory while writing this so I had to stop myself from typing out that outro.)
