A Plebble is undifinable, it is a word that is mysterious and is shrouded in controversy. Using it in an argument results in instant victory for whomever used it and ultimate shame for the other party(s)
Guy1: What you lookin at mate?
Guy2: You, ya Plebble
Guy1: ***commits suicide out of shame***
Dom: That pleb over there just took a shit on the sidewalk! He's only like eight years old.
Jan: Fuckin pleblets need to go shit on themselves instead.