Green’s Dictionary of Slang

(US/P.R.) the buttocks.

1960		I. Freeman Out of the Burning (1961) 127: That bam had drawn a pencilled outline of my chibbs on the bench and printed ‘Frenchy and Florie’ on it.
1979		E. Torres After Hours 24: Spinnin’ full around, hands on hips, showin’ them fine chibs.