Synonymous with "cocksucker," knobnoster is actually the name of a town in Vermont. Easily used an a vituperative, the work "knobnoster" can act as both a noun or an adjective
Not to be confused with the jean noster, a knob noster is when a chick gives a guy a handjob using breast milk as lube. When the guy finishes, she cleans everything up with her mouth, then spits "knob noster" in his face.
When Allison was done giving Adam a handjob with her breast milk, she cleaned off his cock with her mouth, and spit knob noster in his face.