U.S. Olympic legend Greg Louganis -- the greatest diver of all time -- says even world-class athletes like him aren't immune from bullies ... telling TMZ Sports he was mocked as a kid for his last name.
"Loose anus," Louganis says ... "That's what they used to call me."
Greg says he didn't really let the name-calling bother him because he was a kid at the time and chalked it up to kids being kids.
Of course, Greg went on to become a world-famous 4-time gold medal winner, who many believe is the greatest EVER in his sport.
"I mean kids do that," Greg said ... "I can't remember some of the other names from kids in my class. I think loose anus was probably the worst one."