(v.) Another term for cuming or ejaculating. The knob is said “to spit” because it spurts cum with force. And after being blown, the wad looks a bit like spit.
We were in a dark corner, and I spit a full load in my pants when he rubbed my knob.
In hip hop, if someone's got them hot bars, it's common to say they spit crack. Not to say that smokin crack is encouraged, but more like you feel like you're on drugs cause of how dope their spittin is.