This study analyzes how resentment is expressed and shared online through social networking websites. It examines user-generated content on Facebook regarding an incident where an object was thrown at the Italian Prime Minister. The study finds that social media allows proliferation of expressive online communities built around shared emotions. It also finds that while social media amplifies expressions of resentment, it can also play a dissipatory role and facilitate collective rumination of resentment over time. The study develops a model to classify online narratives based on their function (expression vs. action) and level of user involvement (ego-centric vs. hetero-centric).