Boy!

boy

An expression said when one is excited, pleased, or pleasantly surprised. A lot of people sure came to the fundraiser, boy! Boy, that was a delicious birthday cake!
Farlex Dictionary of Idioms.

Boy!

and Boy, oh boy!
phr. a sentence opener expressing surprise or emphasis. (This is not a term of address and can be used with either sex, although it is quite informal.) Boy! Am I glad to see you, Molly!
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • boy
  • boy oh boy
  • Boy, oh boy!
  • howdy
  • boy howdy
  • Boy howdy!
  • oh
  • mama's boy
  • man and boy
  • young man
References in classic literature
'Your hand, my boy! Why have I never heard until the day before yesterday of your suffering yourself to be cooped up in jail?
The Posthumous Papers Of The Pickwick Club
Think how great was his surprise when he saw that the donkey was weeping--weeping just like a boy!
Adventures Of Pinocchio
You're a boy! What's the matter with you?" In teaching, the development of emotional intelligence in youngsters is an essential element of what we need to nurture and this should impact upon how we talk to boys and how we talk to girls.
Link into what's going on in a boy's head, a boy's world and a boy's universe
'You've made a friend for life there boy! Old Pedro's never had so much fuss made of him.' The boy shrugs, drawing up his shoulders, a fluid gesture of defiance.
MORNINGSERIAL