Green’s Dictionary of Slang

jib n.1

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

1. (UK tramp) the tongue.

[UK]Hotten Dict. of Modern Sl. etc. 53: JIBB, the tongue.
[UK]Hotten Sl. Dict. [as cit. 1859].
[[Aus]Australasian (Melbourne) 17 July 8/3: At every step we have evidence of Hindoo origin. For instance [...] Tschib, the tongue [...] is the root' of the word "gibberish," meaning rapidly spoken or incomprehensible talk;.
[UK]Sl. Dict.
[UK]Newcastle Courant 2 Sept. 6/5: He has an oily jibb and is as good at carney as a cackle tub chicken.

2. the face or expression.

[UK]Hotten Dict. of Modern Sl. etc. (2nd edn).
[UK]Hotten Sl. Dict.
[UK](con. 1960s) A. Bennett Untold Stories (2006) 76: Dad looking long-suffering in the back row. [...] ‘Don’t pull your jib, Dad,’ Mam mutters, ‘try and look natural.’.

3. language.

[UK]Sl. Dict.

4. (orig. US Und.) speech, impudent talk.

[UK]Barrère & Leland Dict. of Sl., Jargon and Cant.
[Aus]E. Dyson ‘At a Boxing Bout’ in Benno and Some of the Push 115: ‘Struth, his jibs wouldn’t earn peanuts ez gripman on a mussel barrer,’ said the youth.
[US]Hostetter & Beesley It’s a Racket! 229: Jib [...] frivolous conversation.
[US]L. Stavsky et al. A2Z 57/1: jib – n. talk.

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

[US]K. McGaffey Sorrows of a Show Girl Ch. xiii: Sabrina you certainly do jag my jib to think that you would enter into such a deal.
[US]Daily Trib. (Bismarck, ND) 7 Jan. 8/6: I was wonderin’ what was the pet name in this ’ere court for a biff on the jib! [London Answers].
[UK]M. Marshall Tramp-Royal on the Toby 175: The third was a Lancashire lad with a Borstal cut above his jib.
[US]‘Iceberg Slim’ Pimp 94: He stood over me flashing that gold in his ‘jib’.
[US]C. Shafer ‘Catheads [...] and Cho-Cho Sticks’ in Abernethy Bounty of Texas (1990) 205: gibbs, n. – a person’s lips.
[US]D. Claerbaut Black Jargon in White America 70: jibs n. 1. lips.
[US]O. Hawkins Ghetto Sketches 89: They were the kind of cats who would pinch your nuts off and stuff ’em in your jibbs.
[US]‘Iceberg Slim’ Airtight Willie and Me 16: Her pimp was going to foam at the jib when she checked in that load of play money.
[US]O. Hawkins Chili 50: Reefered to the jibbs.

6. (US black) a tooth; usu. in pl., jibs.

[US]R. Abrahams Deep Down In The Jungle 155: Kicked him in the mouth, bust all his jibs.

In phrases

flap at the jibs (v.)

(US black) to talk wildly, out of control, in a panicky, unrestrained manner.

[US]B. Seale Seize the Time 148: Ballard was running around flapping at the jibs. He didn’t know what he was doing.
flip off at the jibs (v.) [see sense 5 above]

(UK black) to speak in such a manner as to provoke a fight.

[US]Ebonics Primer at [Internet] flippin’ off at the jibs Definition: saying things that will cause you to get your ass whipped. Example: Keep on flippin’ off at the jibs and you gon’ get fucked up out here.
hang one’s jib (v.) [naut. imagery]

to look miserable, lit. to ‘hang one’s underlip’.

[Aus]M. Clarke Term of His Natural Life (1897) 36: ‘P’raps a burial job.’ [...] ‘No such luck. You won’t hang your jib for them yet awhile.’.