A scruffy or dirty person; one who washes rarely.
This derogatory term was coined in the UK in the late 1980s/early 1990s. It was often applied to that itinerant drop-out group the 'New Age travellers', who are also derided as 'crusties'.
The first mention I can find of the term in print is Tony Thorne's Bloomsbury Dictionary of Contemporary Slang, 1990:
"Soap-dodger.., a dirty, unkempt or smelly person, a 'scruffbag' or dosser."
'Dodger' is often used in UK slang. In the 18th century, tub-thumping, ranting preachers were called 'Devil-dodgers'; for example, this piece from James Lackington's Memoirs, 1791:
"These devil-dodgers happened to be so very powerful (that is, noisy)."
More recently, we have seen 'doom-dodgers' and 'coffin-dodgers'; for example, in the 1978 Journal of the Royal Society of Arts:
"Nor am I a doom-dodger or a back-to-nature boy."
and from The Independent on Sunday May 1996, in a piece reviewing a glossary of English/Scottish terms aimed at aiding Americans in reading Irvine Welsh's novel Trainspotting;
"Many of the words explained in the glossary are relatively common British slang - bevvy, dosh, gaff, giro and rat-arsed. But there are plenty that would bemuse most other English-speakers as well: '"biscuit-ersed' (self- pitying), 'coffin-dodger' (senior citizen)."