Green’s Dictionary of Slang

g.b. n.1

[abbr. SE grand + bounce n.1 (5) or go-by n.]

(US) a forceful ejection or dismissal; usu. in phr. below.

as in get the g.b.
[US]E.H. Babbitt ‘College Words and Phrases’ in DN II:i 38: G.B., v.,n. In phrase ‘to get the G.B., i.e. grand bounce,’ to be expelled.
[US]C.H. Darling Jargon Book 14: G.B. – Grand Bounce.

In phrases

get the g.b. (v.)

(US) to be snubbed, to be rejected.

[US]News and Press (Cimarron, NM) 23 Dec. 1/7: Well, I’ve got the g.b. [...] I’ve been fired!
[US]Atchison (Kan.) Globe 24 Apr. 3/4: Well, to use a slang expression, I’ve got the ‘g.b.,’ which means that my services are no longer required.
[US]J. London ‘And ’Frisco Kid Came Back’ in High School Aegis X (4 Nov.) 2–4: Dey tried ter sen’ me ter school — Say! I got de G.B. de firs’ day.
[UK]J. Ware Passing Eng. of the Victorian Era 140/2: Get the g. b. (Amer.). Dismissal – g. b. being ‘go by’. ‘Won’t he feel cheap when he gets the g. b.?’.
[US]D. Malloch Amer. Lumberman in Botkin (1944) 33: He come to camp expectin’ he / Would get from Bunyan the G.B.