Resin Rat
A person that is obsessed with collecting the tarry residue from pipes used to smoke marijuana. This residue gives a mild buzz when smoked and is used as a last resort by some smokers. A resin rat will go to great lengths to get this tarry substance and will even smoke it when bud is present.
Man 1: Wow, Jim is really going to town on that bowl.
Man 2: Yeah, he's a regular old resin rat.
Man 2: Yeah, he's a regular old resin rat.