Green’s Dictionary of Slang

1. (also dill-ball) a small piece of excrement or semen clinging to the hairs around the anus or the female pubic hair; usu. in pl.

1811		Lex. Balatronicum n.p.: Dilberries. Small pieces of excrement adhering to the hairs near the fundament.
1890–1904		Farmer & Henley Sl. and Its Analogues II 286/1: Dilberries [...] Faecal and seminal deposits in the hair of the anus and the female pudendum.
1938		(con. 1892) in Randolph & Legman Ozark Folksongs and Folklore (1992) II 616: D is for dill-balls as big as your prick.
1942		in G. Legman Limerick (1953) 215: A whorehouse at 9 rue de Rennes / Had trouble in luring in me, / Till they got some fairies / With pretty dillberries, / And their clientele came back again.
1989		J. Morton Lowspeak.

2. (also dillberry) a stupid, dull or obnoxious person.

1991		R.G. Barratt ‘Racist Yes, Sexist Fine’ in What Do You Reckon (1997) [ebook] All you need at altitude is for some dillberry to drop a cigarette butt in a bin full of paper towels.
2003		McGill Reed Dict. of N.Z. Sl. 61: dilberry/dill/dillbrain/dilly Stupid person. From the British dialect combination of ‘daft’ and ‘silly’, without necessarily retaining any of the C19 British meaning of ‘dilberry’ as excrement. ANZ mid C20.

3. (also dilbury) a piece of nasal mucus dripping from the bottom of the nostril.

1919

W.H. Downing Digger Dialects 19: dilbury — A dewdrop.