ADJ-GRADED 目瞪口呆的；瞠目结舌的 If you say that you were gobsmacked by something, you are emphasizing how surprised you were by it. 目瞪口呆的；瞠目结舌的 [British, informal, emphasis]
I was really gobsmacked when I saw your picture of a model wearing a hat with a toy airplane on it.