A Greek triple jumper, Papachristou was hours away from realizing her dream of becoming an Olympian. Then, on her way to last year's London Games, she tweeted a joke:
"With so many Africans in Greece, the mosquitoes from the West Nile will at least be eating some homemade food."
Maybe it was supposed to be some kind of play on words. But it was quickly denounced as racially insensitive, or downright racist, by Twitter users.
Greece's Olympic committee condemned the tweet and ruled that she would not be allowed to participate in the games.
For what it's worth, Papachristou's last tweet, from July 25, expressed "heartfelt apologies" for the joke, saying she "could never believe in discrimination between human beings and races."
Sure, Kutcher was already a TV and movie star when Twitter started up. But he became the first Twitter celebrity after joining in January 2009, when the site was getting ready to make the leap from tech-savvy coffeehouse to household name.
He got tons of publicity for becoming the site's first user with 1 million followers -- a distinction he won after winning a race to seven figures with some news network called CNN. He also became a savvy investor in tech startups.
But perhaps more importantly than sheer numbers -- he's now 23rd on the site's popularity list, with almost 14 million followers -- Kutcher seemed to be the first celebrity who understood the benefits of using Twitter to interact with fans.