Disable plugin by itself

How?

PHP:

$this->getServer()->getPluginManager()->disablePlugin($this->getServer()->getPluginManager()->getPlugin("ThePluginName"));

PHP:

$this->getServer()->getPluginManager()->disablePlugin($plugin);

what if he doesn't use a Plugin object in $plugin?

Then he will get an error. My code is correct, or should I write 'Plugin $plugin' in the brackets? That'd be wrong.

$this is already the plugin object...