erb, n. — Green’s Dictionary of Slang

erb n.

[abbr. proper name Herbert, which is seen to be ‘funny’]

1. a wag, a humourist.

1925

(con. WWI) Fraser & Gibbons Soldier and Sailor Words 89: ’Erb: A wag. A funny fellow.

2. anyone whose real name is unknown.

1921

N&Q 12 Ser. IX 344: Erb. Substitute used when a man’s Christian name is unknown.