sexual harassment
Mastodon instances are better than web forums, because if the mods on your instance are assholes, you can go to another instance and still keep in touch with your friends fairly easily.
Whereas jumping ship from a web forum meant losing touch with people or only communicating with them privately from then on.
sexual harassment
Mastodon instances are still vulnerable to trolls account hopping, but users are at least empowered to block and mute...instead of having to wait around for a problem user to get banned.