Wiktionary
swap spit
vb. 1 (context idiomatic slang English) to kiss, to make out 2 (context idiomatic slang English) to exchange information
Usage examples of "swap spit".
He was halfway to the floor, frantically scanning the room for a shooter, reaching for his own piece, when he saw that both she and her boyfriend were under the table, thumbs jammed in their ears, mouths wide open like they were fixing to swap spit or something.