They used to say that actions speak louder than words, but in today's world both your actions and words can live on forever. Recently, Ariana Grande has been blasted for saying "I hate America" in a short video clip (after a store clerk told her not to lick a doughnut).
If you recall in December 2013, Justine Sacco (a PR staffer at the time), tweeted something pretty racist before getting on a plane to Africa. By the time she landed, not only had she lost her job, but earned herself thousands upon thousands of hate-tweets and subsequently had to delete her account.
On some deep level, we know people have the capacity to say dumb things sometimes. Things they may not really mean, but in a heated or stressful moment will blurt out sans-filter. Only today, if you do it on social media, it can never be deleted or taken back. Even deleting your entire online presence will not take care of it, because someone, somewhere, took a screenshot a second before.
Before you post anything for the world to see, ask yourself if you would be proud of it tomorrow, next month, or if you would repeat it to your grandchildren years from now.