Let's cut the bull. Some researchers on Fark recently discovered the actual origins and likely history of the HA! HA! Guy.
To date we knew that the HA! HA! Guy originated from a turn of the nineteenth century advertisement for Forbes' Insoluble Dry plates. We know that dry plates are used for photography and not a colonial slang term for dentures. Everything else you've ever heard about the HA! HA! Guy was either legend or made up purely for our own amusement.
New Information
Discovered in the depths of teh Interwebs was a Goodwill Auction for a painting of a "Midland Man 1874" that looked eerily similar to the HA! HA! Guy.
Decide for yourself:

The back of the painting reads "The man who resigned a Midland position in 1874 and got his pay"A quick Internet search on Midland 1874 reveals that there was a Canadian railroad company, the Midland Railroad, that suffered severe financial troubles in 1874. Perhaps the HA! HA! Guy was a manager who pulled an 1874 Enron?
'Midland 1874' may also refer to a series of locomotives manufactured in England, a strip of track laid in the Western part of the United States, or possibly an Illinois railroad company that foreclosed that year.
This is epic. Not only do we have digital proof of this amazing, full color painting of the original HA! HA! Guy, but we have a another shred of evidence linking us to his origin.
The HA! HA! Guy is the Midland Man reincarnate.
Do you have more information? Email TDQ! because we want to know!
