From Public Enemies, America’s Greatest Crime Wave and the Birth of the FBI 1933-34 by Bryan Burrough. Pretty Boy’s picture is right below Machine Gun Kelly and his wife Katherine. Kelly looks more like a young Rodney Dangerfield to me, but even so, at least in this picture out-pretties Pretty Boy.
According to Burrough’s book, no one but the newspapers called Charley Floyd “Pretty Boy.” If any of his associates called him Pretty Boy they didn’t say it to his face, but it struck the public imagination, and that is how we know him now.
From Crime Does Not Pay #51 (1947).