Green’s Dictionary of Slang

1. a tout, also as v.

1884

4 Oct. 3/4: ‘To business — let us go out to Brussels.’ ‘To Brussels?’ ‘Yes, to Brussels-sprout, you know, to tout’.

2. a Boy or Girl Scout.

1911		J.W. Horsley Memoirs of a ‘Sky Pilot’ 253: The children gave me such words as [...] ‘brussel-sprout’ for boy scout.
1936		Motherwell Times 3 Apr. 5/6: The Boy Scouts and Sprouts and the Girl Brownies.
1949		Northampton Mercury 8 July 7/4: The girl Scouts — Brussel sprouts as they were nicknamed — were [etc].
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 373: Leslie Paul remembers, before the First World War, a mob of spitting youths around Aldgate jeering: Here comes the Brussel Sprouts, / The stinking, blinking louts.
1962		K. Waterhouse There is a Happy Land (1964) 25: He was in the boy sprouts.
1976		(ref. to 1930s–70s) R. Barnes Coronation Cups and Jam Jars.
1980		Barltrop & Wolveridge Muvver Tongue 65: There was no verse for the Boy Scouts – perhaps ‘Brussel Sprouts’ said it all.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.

3. (Aus.) a lout.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 21: Brussel Sprouts Louts.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Brussel Sprout. Rhyming slang for lout.

4. a term of affection [= old scout under scout n.].

2002

K. Lucas ‘All my life I’ve wanted to be a Barrow Boy’ Obfuscation News Apr. Issue 20 🌐 ‘No worries my old Brussels Sprout’, he croaked taking his Oxford Bag out of his North and South and Daren Coughing like mad.