Hashtag activism isn't new; people have been using Twitter as a medium to communicate social change for as long as the service has been around. Regular plebes may be able to get away with a few politically charged tweets that disappear into the void that is the Internet, but celebrities are afforded no such luxury.
As dismal developments of the Israel-Palestine conflict continue to roll in, most people are inclined to take a side. Rihanna decided to chime in by posting #FreePalestine, but quickly deleted the tweet. TMZ reported the singer claimed she didn't know she tweeted it, but without a direct a quote from her it's hard to discern what her motivations were.
Then again, the Internet has no mercy for misguided Twitter behaviors of celebs, with many commenting on Rihanna's actions.