To swap spit, like making out. It is a form of oral sex - fluid exchange takes place, in the form of saliva.
Jenkin and Jessica were spit kissing so intensely they had each other's saliva running down their cheeks.
Jenkin: You're hot.
Jessica: (slobbering) I know, right?
(start slurping up spit from each other's mouth)
February 20, 2013