Brick oneself is British slang for being terrified or extremely nervous. "I was bricking it." Vulgar origin (referring to soiling one's pants from fear). Not concerning, just informal British vocabulary. If your kid uses it constantly, ask them where they first heard it, not to police their speech but to understand which online community they are in. Most slang of this kind moves through TikTok and group chats, so seeing it in your child's vocabulary just means they are plugged into normal teen internet culture.