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1.
An expession Newfoundlanders use which could show the emotions of amazement, disbelief, agreement, etc. and also can be very sarcastic.
"I got so loaded last night I fucked my cat"
"Yes b'y!"
by shanty for the arethusa March 04, 2006
 
2.
Newfie slang, expressing disbelief or amazement.
" I want a gold toilet"
"yes b'y"

or

" My cat just had puppies"
" yes b'y"
by Emily April 25, 2005
 
3.
Newfy slang to express affirmation or assent or to mark the addition of something emphasizing and amplifying a previous statement
Would you fuck her?
Yes by!
by The Mac February 09, 2012