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1.
verb

1. Whilst pumping; to grit one's mouth in pure concentration and "spit" from one's reproductive organ.
"Shit there's nothing on the TV! Nothing else better to do, I may as well grit and spit."
by Thom Allan January 26, 2007
 
2.
to "grit and spit" derives from "gritting" whilst performing masterbation and "spitting" after performing masterbation.
that boy don't do nothing all day he just sits there in his room staring at the tv smoking pot and nothing else but grit and spit.
by Sharaku Kobayashi December 27, 2007