There is slick Argentine fellow named Cesar Rene Cuenca who is fighting for the vacant IBF light-welterweight strap. He is 47-0 with 2 knockouts. He punches with proper technique but he just can't crack. His countryman Nicolino Locche had a hard time hurting men too. He had 14 stoppages in 136 bouts.
You can see a youtube video where Byrd does an experiment where his punches are recorded before & after abstinence. He allegedly hit hard on the machine, something over 1200 PSI... I vote for Stephen Hawking. Watch out for that Hawking radiation though.
Calderon worked at a waste management facility and his co-workers nicknamed him "Little Tyson" because of his alleged power. They were way off, obviously. Great little fighter was Calderon though.