"Imagine wasting your time and energy persecuting merpeople when there are little toerags like Kreacher on the loose -"
- Sirius, speaking of Umbridge's record on part-humans (OP14)
A worthless, despicable person.
U.S. readers may have already encountered this one in Douglas Adams' The Long Dark Tea-Time of the Soul as the name of one of the characters (Odin's nasty little sidekick).
This comes from an older sense referring specifically to vagrants, which in turn comes from, well, a person who uses a rag wrapped around the foot instead of a sock. (NSOED).