Green’s Dictionary of Slang

(US) affectionate term of address used by one man to a (younger) one.

1878		A. Pinkerton Molly Maguires 34: ‘I’ll e’en do better by you, me laddy-buck’.
1884		Grip (Toronto) 16 Feb. n.p.: But, me laddy buck, where’s the money to come from?
1891		Life Jan.-June 130: All right, me gay laddy-buck. You can take your choice.
1902		J. London Daughter of Snows 177: ‘No ye don’t, ye young laddy-buck,’ he interposed.
1935		J. O’Hara Butterfield 8 90: Did you never hear of the Civil Service, my laddy-buck?
2013		C. Peck Ranch 30: Laddy Buck was one of the nicknames he had for me ; Laddy Boy was another , but that one always made me feel like a can of puppy chow.