The Homeboy Alonso Cisneros has got to be one of the worst fighters I have ever seen. Watch the fat mess struggle against some random bar fly making his debut This content is protected
There are obviously worse fighters, but in terms of people who somehow managed to get pretty high-profile fights on the world stage, I've found Mark De Mori to be spectacularly bad. After looking totally out of his depth 10 years ago vs Haye, I had to do a double-take when he somehow got on the Saudi card vs Hrgovic, which of course went much as expected. I'm not sure he'd be able to withstand Peter McNeeley's legendary 'Cocoon of Horror' bum rush.
There are fields and fields of bad fighters so I think the better question is "the worst fighter that had name recognition" I would say that Mario Cawley is probably the worst ever. Mario Cawley was undefeated then started losing..................and literally never won again. That takes a lot of effort