An exclamatory used in a situation in which you cannot find words to express the current state of being.
Used also in dire situations in which sentences cannot be formed quickly enough to convey your thoughts.
Used also in cases where thoughts are irrevocably passing through your mind vis-a-vis random instances; ergo you are forced to salvo in a tumultuous manner, "MAGOO!"
Did you see that boy with the mushroom stamp on his forehead?! MAGOO!!
It was just, i mean she was like, and it was... AH MAGOO!!!