@Podi125
It wasn't meant to be like a full effort crossplay. Pretty sure he was just there to intimidate annoying male followers from stalking the girls. The simplicity of his costume is likely because no one will care about what he is wearing if he is just glaring at them the entire time. Also he likely chose it specifically just for the memes.
Goujo felt threatened not by his costume, but by the confident way he carried himself. Goujo has actually a fairly weak sense of confidence, which usually goes unnoticed when it is just him and Marin, since he can just focus on the work at hand. But when alone and out of his element, he becomes incredibly self conscious which stems from an instance of past trauma involving doll making, which this cosplay gig is more or less an extension of, plus adding on the blurring of the usual gender lines that commonly come with it. One bad comment can easily ruin a person's self confidence, especially if it is a girl telling it to a guy. Boys often take that shit to the grave, because it just doesn't happen that often, where just anything someone comments about you, regardless of it being a compliment or a criticism, they can't easily forget it.
If you are a girl and want to ruin a boy's self value, as long as he isn't a complete chad where he doesn't give a fuck about what anyone says about him, just make on direct criticism about his person, or one of his interests that picks at his identity. Such as saying he creepy. It may ruin his entire self esteem for years, even if everyone else says otherwise. (Seriously though don't do this.)