Green’s Dictionary of Slang

1. the best, the superlative.

1908		K. McGaffey Sorrows of a Show Girl Ch. ii: Say, that piece of work that stands on the end opposite you is all to the berries, ain’t she?
1917		J.E. Rendinell diary 12 Nov. in One Man’s War (1928) 33: I growed a moustache [...] I thought it was the berries.
1926		Van Vechten Nigger Heaven 157: She’s the berries at that, was Olive’s comment.
1937		T. Thursday ‘Good Luck is No Good’ in Federal Agent Nov. 🌐 In brief, Mr. Todd had an idea that he was the berries minus the razz.
1941		P. Cheyney Your Deal, My Lovely n.p.: Except for the fact that she hadn’t had her face lifted she mighta been your favourite film star. That baby was the berries.
1942		W. Winchell ‘On Broadway’ 19 Nov. [synd. col.] Phillips [...] cabled his adored [...] ‘This is the berries’.
1951		Cusack & James Come in Spinner (1960) 297: He was simply the berries.
1959		M. Richler Apprenticeship of Duddy Kravitz (1964) 199: This is the berries.
1967–8		Baker et al. CUSS.
1971		T. Murphy Morning After Optimism in Plays: 3 (1994) Scene ii: I could have been the very best. Why they napped me to be the berries in my trade!
1979		H. Leonard A Life (1981) Act II: Is this the berries or isn’t it?
1989		H. Leonard Out After Dark 99: ‘Tell the truth, is she the berries or is she not?’ he asked, pink with pride.
1994		L. Bergreen Capone 318: There had never been an outlaw quite like Al Capone. He was elegant, high-class, the berries.
2003		McGill Reed Dict. of N.Z. Sl.
2015		L. McInerney Glorious Heresies 77: ‘Aw stop, aren’t you the fucking berries?’.

2. as a negative, the ultimate, the last straw.

1929		W. Winchell On Broadway 3 Oct. [synd. col.] The too much sunburn theory is strictly the berries.
1937		P. Cheyney Dames Don’t Care (1960) 7: Say, this town is the berries.