Extract revised for OED Online

dog, n.¹

DRAFT REVISION July 2007

dog's bollocks n. (also dog's ballocks) Brit. coarse slang (a) Typogr. a colon followed by a dash, regarded as forming a shape resembling the male sexual organs (see quot. 1949) (rare); (b) (with the) the very best, the acme of excellence; cf. the cat's whiskers at CAT n.¹ 13l, bee's knee n. (b) at BEE n.¹ 5b.

    1949 E. Partridge Dict. Slang (ed. 3) 1033/2 Dog's ballocks, the typographical colon-dash (:—). 
c1986 in P. BREWIS et al. Gambler (cassette tape sleeve notes) They are of the opinion that, when it comes to Italian opera, Pavarotti is the dog's bollocks.

1989 C. DONALD et al. (title) Viz: the dog's bollocks: the best of issues 26 to 31. [sl] 1995 Times 4 Oct. 7/1 Before Tony Blair's speech, a chap near me growled: "'E thinks 'e's the dog's bollocks.' Well he's entitled to. It was a commanding speech: a real dog's bollocks of an oration. [inc] 2000 Front Oct. 51/3 You said you quite fancied Jon Bon Jovi. Yeah, Jon Bon Jovi is the dog's bollocks.