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.