An exclamation of surprise, irritation, emphasis, etc: Good night! Must you chew that gum so loud?
[1880s+; a euphemism for good God]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with good night
Expression of farewell used when parting at night or when going to sleep, as in He stood at the door, saying good night to each of the departing guests, or Mother came to tuck the children in and kiss them good night.
[ Late 1300s
Exclamation of surprise or irritation, as in Good night, Joe!—You can't mean what you said, or Good night, Anne—it's time you learned how to throw a ball.
[ Late 1800s