... Canelo Alvarez
... Miguel Cotto
... Juan Manuel Marquez
... Arturo Gatti
... Ricky Hatton
... Zab Judah
Tomato cans, the whole lot of them.
The Judah fight, the one where Mayweather's father climbed in the ring to go after Zab Judah?
Or the Gatti fight, the one where Mayweather didn't make weight and paid Gatti to fight anyway?
He made Hatton move up to fight at 147, after agreeing at first to drop weight to fight Hatton at 140, where Hatton was better.
Oh, and he was out boxed by Castillo in the first fight, and the judges bailed him out. Few people outside of raging Mayweather fans (and they exist, its like listing your favorite color as "beige) think Mayweather won that fight.
As far as listing people he did fight, you may as well list people he wouldn't fight, starting with Margarito (chose instead to fight post-fishnet and heels De La Hoya, who was a joke).
Or this writeup, courtesy of the internet.
In 2005, Mayweather called out Winky Wright, the lineal and formerly undisputed 154lbs title holder who had just beaten Felix Trinidad at 160lbs and could point to two wins over Mosely. Wright agreed and within days had his team in the Top Rank (Floyd's promoters at the time) offices hammering out the details.
The details were hammered out: the bout would be at 154lbs but weigh-ins would be the morning of the bout rather than the day before and Wright would not be allowed to gain more than eight pounds between weighing in and the start of the contest. But Mayweather and Bob Arum suddenly pulled out, demanding changes to the purse-split and other such things until the bout was dead in the water.
Mayweather was brave to challenge the naturally larger Wright, a man basically in his prime and with a style that would have been awkward for Mayweather. But when you call someone out and agree all of the details, why then suddenly pull out and take on Sharmba Mitchell instead? That's ducking. Whether it was Arum or Mayweather who pulled the plug (Wright's promoter Shaw has blamed both Arum and Mayweather, depending on who was asking) it doesn't matter; it was a duck.