To put effort and enthusiasm into a blow job.
My manager gave me a raise, I'm gonna spit shine that cock.
Using ones own saliva to give something, or someone (if you're into that) a shine that's so lustrous it makes Jesus himself turn away from its blinding reflection.
"Hey Tom, how'd you get your car so shiny?" "I can't even see."
"I spit shined the shit out of it and it really paid off."
Unbelievably clean.
Joe's new Lambo was sitting there spit shined in his driveway.
An object that is most likely brighter than your future.
That man spit shined his shoes till they were brighter than my balls dipped in Vaseline.