Cockney Rhyming Slang - Dicky Dirt

As far as I can tell, there was no actual person called Dicky Dirt. Perhaps he was a music hall character, or perhaps a reversal of the name of the 18th Century Dirty Dick who inspired the name of the old pub in the City of London, Dirty Dick's.

So whatever the origins 'dicky dirt' is a shirt.

Here we have a picture of Nathaniel Bentley, the original dirty Dick

More Bentley stuff here.