Obsolete British insult: a toerag is a piece of cloth worn on the foot under
the boot to substitute a sock, especially in winter, and by vagrants. Something that is
squalid and disgusting; by extension, a bum,
vagrant or tramp.
Preceded more obscene (and thereby effective) insults such as tosser or wanker. It has fallen into disuse also because it invokes an element of the old class system, snootishness and looking down your nose at the lower classes.