  The act of Slobbing Knob is performing felatio on someone else. This has become a slang termonology in the rap community over the discourse of East-Coast Rap.
Popularization[]
The first account of a rapper spitting a line with Slobbin' Knob is Grym Reaper of the Gravediggaz on the song "Hidden Emotions" where the rapper say's "you either rap or rob/and girls slob knob/ and N***** sell crack, weed, dope, for the mob."