Green’s Dictionary of Slang

exceptionally and overtly friendly, prob. insincerely so.

1944		J.M. Inks diary Eight Bailed Out (1954) 28 July 35: I don’t like the idea that these people are buddy-buddy with the Krauts.
1955		Kerouac letter 18 Jan. in Charters I (1995) 459: Joan and my woman probation officer real buddy buddy shaking hands.
1965		(con. 1944) E.M. Nathanson Dirty Dozen (2002) 152: He might have laughed at Franko’s buddy-buddy act.
1977		L. Heinemann Close Quarters (1987) 269: People been pounding that buddy-buddy shit up my ass half a my life.
1983		S. Gee Never in My Lifetime in Best Radio Plays (1984) 59: It’s called the buddy buddy system. Cuddle up for warmth.
1999		Guardian Media 14 June 9: The advertisers can get on buddy-buddy terms with the consumers.
2000		N. Barlay Crumple Zone 127: I see Dennie: everyone’s friend, buddy buddy with Fergal.