Such an iconic scene in Haruhi anime.
Also love that shopkeep was like, "where did this gyaru pop out from and why is she here?" Honestly though, some of the adult/married gyaru-ish IG influencer subset I follow (if you ignore the occasional overdone nails, then the outfit and rest of the appearance are often clean lines and usually casual/street styles that feel grown-up, a mix of Uniqlo/Gu and luxury brands and not like they stepped out at Shibuya station) do cosplay every so often. I suppose knowing how to do makeup and hair, having access to nice clothes/cosplay outfit makers, and being happy to do photo shoots isn't all that much of a stretch. Plus the power of role play and suggestion I'm sure helps maintain their following.
Finally, it's not like Gojou is totally unaware, he's just grown up a little socially awkward and has that artisan/craftsman mindset where he gets into a flow. I'm sure love and relationships (and a muse) will further awaken his power/skills/determination/fetishes.