Green’s Dictionary of Slang

(US) kissing and cuddling in public.

1968		Current Sl. II:3 5: PDA, n. Public display of affection.
1970		Current Sl. V:3.
1981		Z-Link 30 Oct.–1 Nov. 🌐 Not the place for P.D.A., but if she leaves with you, you’ll at least get to swap spit.
1995		J. Stahl Permanent Midnight 27: I just wasn’t down for any form of PDA (Public Display of Affection).
2006		Sam and the City at blogs.smh.com.au 20 June [blog] Commonly known as PDA (public displays of affection), flaunting your lust in front of a bunch of strangers can wreak havoc among those around you.