Well he wore it because Roger Mayweather was known as the "mexican assasin" for a period in his career & used to wear an outfit like that to the ring.
Here is an article I found on it.
ROGER MAYWEATHER AND HIS DAYS AS THE " MEXICAN ASSASSIN " by Ted Luzzi Apr 14, '06 11:58 PM
by Jim for everyone
neverlast
The recent brawl and the involvement of Roger Mayweather reminds me of a time Roger was a fighter and stirred the boxing world of Los Angeles. It was all good natured at that time (unlike the ugly scene at the recent fight) and one of the best jobs of marketing boxing I have ever seen. Oscar Bejines was one of the most popular Mexican fighters at the Olympic in LA He had a 32-3 record and was a real crowd puller.A boxing craftsman who had it seemed seen better days but still a big name ,Roger Mayweather was brought in to be whipped by Bejines and add another well known name to his record and maybe earn Oscar a title shot. In his last 10 fights, Roger had been KOed in one round by Rocky Lockridge and then KOed in 2 by Julio Caesar Chavez and lost to Tony Baltazar . In his last 10 fights he had 4 losses including his last fight when he was KOed by Freddie Pendenton. A big name on the skids was exactly what the promoter wanted. However fight night was a surprise! The unpredictable Mayweather stunned the home-town rooters and KOed the popular Bejines . Well at the historic Olympic these things don't go unavenged. Segio Zambrano a fighter with a 34-1 record was brought in to teach the "Black Mamba" a lesson . Zambrano had had up until that time all his fights in Mexico. . It was figured that it would be a great introduction for his first fight in the United States to be at the Olympic and against Mayweather who had beaten Bejines. Mexico's rabid boxing enthusiasts turned out to see the exciting new fighter and also see Bejines get revenged. It all was just one month later. Mayweather showed fight -stopping power that night and TKOed Zambramo in 6 rounds! Just when everybody was ready to close the book on his career here he is beating two good Mexican fighters. Mayweather dubbed himself (or somebody did anyway the "Mexican Assassin" instead of the Black Mamba) and fought over the next year three non-entities and then lost to Pernell Whitaker to it seemed finally end his time in big time boxing. However though he lost to Whitaker (who had only 11 fights at that time) there was the matter of Mexican revenge. Rene Arrendondo was the WBC Super Lightweight champion and a thunderous puncher if there ever was one. Mayweather had a punch good boxing skills but a weak jaw. The scene was set.The Los Angeles sports arena was filled with rampant Latinos and the fight was even for the title. Why did Mayweather get a title shot after losing to Whitaker ? Hell the Mexican and Latin fans wanted to see him get flattened and would pay for it. I was around and often visited L..A. in those days. It was all good fun . Mayweather was the guy they loved to hate but they kind of liked him too. The fans hooted and waived programs at Mayweather when he came down the aisle.The fans were excited over the impending Mayweather defeat. Arrendondo was fighter with over 40 wins and won the title over another big talking fighter Lonnie Smith with one big punch at the Olympic . He was expected to do the same to Mayweather. Roger the newly named "Mexican Assassin" entered the arena and Mexican fans were stunned. Roger of course is a black guy ond their sitting on his head was a huge all black Sombaro ! The boos were loud and long. Worst yet for the fans, Worlds champion Arrandondo was beaten by a exceptional ring performance by Mayweather that night. In round 6 he was crumpled to the canvas three times and wonder of wonder Mayweather was the champion and another Mexican hero was wiped out ! Twice more in 1988 Mexican fighters were brought to fight Mayweather. However these were Muricio Aceves and Rodolfo Gonzalez (who had lost 2 of his last 4 fights) Mayweather beat them both but the joke was wearing thin by then and the Mexican fans wanted a winner. Roger also defended the title twice outside of Los Angeles winning a hairline decision over tough Harold Brazier and a solid win over Vinny Pazienza.
Who was brought in to finally take care of Mayweather ? None other than the lion of Mexico Julio Caesar Chavez himself! With a 63-0 record and general recognition as the best fighter in boxing . Your going to get it tonight Roggggggggggerrr! yelled the Mexican fans on fight night. Mariachis merrily played , fireworks went off in the stands and the big crowd bubbled with enthusiasm . . No way Julio would let them down. . Chavez took care of business. Cries of "Mejico, Mejico" filled the air as he won the fight easily giving Mayweather a solid thumping. However the Mexican fans cheered Mayweather too for staying in there and fighting until it was stopped in round 10. The "Mexican Assassin" went back finally to being the Black Mamba as Chavez was lifted in the ring and there was great carrying-on. A good natured rivalry not like the ugly scene at the fight the other night and a good memory for me of that time