In the age of social media, why do some people still do bad things in public?

A woman wrote something disgustingly racist on her receipt at a restaurant. The server took a photo of it, found her Facebook page and workplace, and made a viral post urging everyone to notify her employer of her behavior. Said woman is now fired. In the age of social media, anybody can find our whereabouts and affect our livelihood; how can anybody be dumb enough to be openly disgusting and racist?