Green’s Dictionary of Slang

grab-ass n.

[SE grab + ass n. (2)]

(US) fighting, fooling around.

implied in play grab-ass
[US](con. 1950) E. Frankel Band of Brothers 18: Knock off that grabass!
[US]H. Rhodes Chosen Few (1966) 44: No noise, no laughing, no grab-ass under penalty of the DI’s wrath.
[US](con. late 1940s) E. Thompson Tattoo (1977) 651: He quit all grabass in the barracks, pursued his job.
[US]L. Heinemann Paco’s Story (1987) 179: There was considerable jostling and arm punching, jawing and grab-ass back and forth.

In phrases

play grab-ass (v.)

1. to fool around.

[US]Heggen & Logan Mister Roberts 430: You’ve been getting pretty smart playing grab-ass with Roberts here [...] but now you’ve gone too far.
[US]K. Powers Yellow Birds 56: The children began moving along the walls, most giggling and playing grab-ass.

2. (US) to make physical advances towards someone.

[US](con. 1950) E. Frankel Band of Brothers 4: That’s right. Play grabass! I told you to watch the village.
[US](con. 1940s) M. Dibner Admiral (1968) 356: Drunk as slobs, playing grabass with the greasy gigolos.
[US] in J.P. Spradley You Owe Yourself a Drunk (1988) 57: Those punk cops are busy playing grab-ass — they’re all queer.
[US]L. Shecter On the Pad 84: [W]e pick up these two broads from out of town. My buddy is up in the hotel room with the other one, and I’m stuck down in the car playing a little grab ass.
[US]H. Rawson Dict. of Invective (1991) 28: play grab-ass. To fondle, not necessarily the buttocks, in extended use, to fool around.
[US]D. Simon Homicide (1993) 559: Boy finally gets sick of playing grabass.
[US]F.X. Toole Pound for Pound 278: They laughed and kissed, and played some grab-ass.
J. Shaw ‘Luck’ in ThugLit Sept./Oct. [ebook] A group of drunk dudes playing grabass.