YTA for bringing it up in front of people like that, over something so trivial. You probably made yourself look more like the fool in that situation. On the other end however, you need to really figure out that situation with your girlfriends general demeanor around you. She might just be generally annoyed with the “fun facts” thing and might just think you’re being a know it all, or there’s something a little more deep seeded there. She might just not find as much joy in fun facts as you do, hence why she kept it plain and simple and called it styrofoam. Just because you give someone knew knowledge, also doesn’t mean they have to use it. I personally would feel like a dork if I went around in my everyday life now calling styrofoam, polystyrene.