From the raw, it seems like she was accusing Nitanda as someone who uses online slang a lot. (I haven't seen the raw for previous chapters, so I don't know if he actually used it).
I think translating『エグいって』as "That's crazy" is too tame. According to AI, it does mean that. But it's a slang that kinda breaks the original word.
I'm kinda old, so I don't know what kids use these days. But I guess it's like saying "cray" for crazy?
Again though, I haven't checked whether he actually uses that often or not.
I kinda suspect that everything she said about Nitanda in this chapter was meant to insult him and disparage him in front of Yukide. There's every chance he
has used slang of that nature before (haven't looked at the raws myself), but....contextually, he just doesn't come across as the type, at least in terms of the every chapter we've seen up to now.
Maybe "online-meme mode" is something different than I'm interpreting, but stuff like simply responding to things like "that's crazy!" evokes a sort of ...I guess 'vapid' personality, who engages with things at the surface-level, at most, especially using the example given in this chapter.
Nitanda comes across as way too introspective and thoughtful about things. He made a video for her birthday out of dominoes
at least weeks if not months before-the-fact, just so he'd have it ready when he needed it. And he was so awkward in this chapter with Yukide precisely because he was too deferential to her the whole time.
Everything else Machino did this chapter, leads me to suspect she said that simply to make him look bad. She had none of her usual playfulness about her this time, opting instead to make every word of Nitanda critical or insulting, and then promptly took Yukide from the room and ended the chapter with the only "goodbye" her sticking her tongue out at him after calling him a repressed nerdy pervert, and giving him no chance to explain himself.
None of that matches her tone anywhere else in the series to date. We can speculate on her reasons for doing so - such as her being jealous that he was spending time with a girl who wasn't her,
alone no less - but Machino was outright antagonistic toward Nitanda this time. So everything she said to him, seems like a fabrication.
Charitably, she said it all simply to make him seem "not attractive(???)" in Yukide's eyes, to ward off a potential rival (again, ???) - but that's me hoping the author has just decided to fall back on old tropes and gimmicks that are prevalent to the genre, and not that Machino's turned a corner into being an actual bully to Nitanda for whatever reason.
Hopefully next chapter explains things or at least sheds some light.