I have dealt with many disputes involving popular stars, and a large number of them involved netizens impugning celebrities' reputations.
There is a phenomenon on social media - for example, the microblogging site Sina Weibo - where fans of certain celebrities attack other stars who have the same characteristics as, or are rivals to, their idols, and also attack their fans.
They insult the celebrities by posting and forwarding abusive messages, and some even libel them by maliciously fabricating and spreading false information.