Green’s Dictionary of Slang

jib n.1

also jibb
[Rom. chib, jib, the tongue; Hind. tschib, language]

1. [mid-19C] (UK tramp) the tongue.

2. [mid-19C] the face or expression.

3. [mid-19C] language.

4. [late 19C+] (orig. US Und.) speech, impudent talk.

5. [20C+] (US black, also gibbs, jibbs, jibs) the mouth [dial. jib, the underlip; thus the mouth].

6. [1950s–60s] (US black) a tooth; usu. in pl., jibs.

In phrases

flap at the jibs (v.)

[1950s+] (US black) to talk wildly, out of control, in a panicky, unrestrained manner.

flip off at the jibs (v.) [see sense 5 above]

[2000s] (UK black) to speak in such a manner as to provoke a fight.

flying jib (n.)

[1910s–60s] a talkative person.

hang one’s jib (v.) [naut. imagery]

[late 18C–19C] to look miserable, lit. to ‘hang one’s underlip’.

slide one’s jib (v.)

[1930s–40s] (US black) to talk unrestrainedly.