Drug user who searches carpet for lost drugs ("Shards" of Crystal Meth) while on hands and knees, not unlike an Ardvark. Someone who solicits free drugs to maintain their addiction.
ie: Tell Larry to quit shardvarking because it makes me nervous. Don't be a shardvark or you will have to leave. I can have her shardvark for it if it bounced under the table. They're both shardvarks and you can't trust anyone who's that deperate to get high or maybe they're shardvarkians from "Planet Crystal".