2012 London Olympics athletes have been banned from posting x-rated tweets, the International Olympics Committe has ruled. It has however, allowed the athletes to tweet in first person diaries and post still images using no "vulgar or obscene words or images". Athletes tweeting for commercial purposes similarly face a withdrawal of their accreditation, effectively a ban.
Athletes are also disallowed from reporting in journalistic style and posting camera-phone videos. The new rules are likely to curb more artistic efforts on part of the athletes, restricting them to straightforward diarised expression. However, since journalistic styles vary and "vulgar words" and expressions may be context dependent, it appears the IOC will have under its own control to ban whatever it defines or deems to be offensive.
Social Media restrictions were more tighter in the 2008 Beijing Olympics where the athletes were not allowed to share images and videos. British triple Jump athlete Philips Idowu caused controversy, recently, when he tweeted that he won't participate in the European Team Championships, without informing his team in advance.