Green’s Dictionary of Slang

(US black) to kiss, to engage in heavy petting; thus slobbing n.

1904		Number 1500 Life In Sing Sing 253: Slobbing. Kissing.
1924		G. Henderson Keys to Crookdom 417: Slobbing. Love-making.
1949		Monteleone Criminal Sl. (rev. edn).
1972		D. Claerbaut Black Jargon in White America 80: slobbin’ v. lightly hugging and kissing; necking.