Green’s Dictionary of Slang

pec n.

also peck
[abbr.]

usu. in pl., a pectoral muscle, the development of which is popular among body-builders.

[Can]L. Cohen Beautiful Losers (1970) 159: I saw you with massive lower pecs and horseshoe triceps, with bulk and definition simultaneously [OED].
[US]L. Kramer Faggots 18: What had at three feet appeared to be well-formed pecs (so important), at two feet were revealed as sagging tits.
[UK]Kirk & Madsen After The Ball 314: By being terrific in bed? [...] By having pecs or thighs of death?
[US]T. Willocks Green River Rising 229: Sweat ran down his throat and into the shallow cleft between his pecs.
[US]J. Franzen Corrections 52: Denise in the photo was wearing jeans and a tank top and was all muscled shoulders and satiny pecs.
[US]R. Price Lush Life 66: Taking a step back and palming his pecs .
[Aus]P. Temple Truth 55: The front-seat passenger stuck his gun out [...] fired four shots, took away a big piece of Colby’s right pec, a bit of an ear.
[US]J. Stahl OG Dad 61: Some grinning douchbag driving a convertible while removing hair from his pecs.