Floyd Mayweather has taken a swipe at boxing legend Muhammad Ali and ranked himself as the greatest boxer in history. The former pound-for-pound No.1 retired from the sport in 2017 following his win over Conor McGregor which took his record to 50-0. Speaking to ESPN, and referring to himself in the third person, Mayweather brags about fighting more world champions and winning world titles in five different weight divisions. ‘He’s beat more world champions than any other …