You clients are always using the crappy visual editor in your WordPress? They always paste shitty formatted texts from the internet? They also edit your posts and fuck it up? Then you should try this plugin.
Disable WYSIWYG sets user_can_richedit to false that disables TinyMCE Visual Editor (WYSIWYG editor) totally completely permanently forever. This plugin also works fine with multisite enabled WordPress (aka. WordPress Mu). If you love this plugin, please consider buying me a cup of coffee.
Download it at WordPress.org