Visit Doc Morbid's hospital, climb down the ladder into the doctor's basement and meet a mentally-challenged worker of diminished stature named Gretch. He will not so subtly let it slip being hard at work sorting out some human body parts to send to Iguana Bob in the Hub.
If the Vault Dweller confronts Doc Morbid over it, nothing will happen and they cannot tell the authorities, leaving little opportunity for justice to be served. If the player kills Gretch, however, the Doctor and his two bodyguards, Flash and Cougar, will attack. No one will be bothered by their deaths, though.
The Dweller then needs to go to the Hub and find Iguana Bob's stand in Downtown. A high Speech skill is needed to frighten him enough. Depending on Barter skill, Bob can be blackmailed for a large slice of his profits. Renegotiate with an increased Barter skill for even more profit. This number can go virtually unlimited bottle caps with lots of patience, but Reputation will plummet accordingly.
When trying to blackmail Bob into paying the player character, one of the dialogue options is to scream "Prime Choice Select is made of people!!!! It's made of people!!!". This is a reference to Charlton Heston's famous line from the film Soylent Green in which his character realizes a similarly morbid cannibalistic truth.