So since some people have a distaste for followbots, I have added a feature to !postActiv to allow people to filter subscribers against a Perl-compatible regular expression.
To set it, put this in your config.php:
$config['site']['sanctions']['subscriptions_filter'] = "PCRE goes here";
Then any user who tries to subscribe to you who matches the filter will receive an authorization error and will not be able to subscribe.
Of course, be careful with what PCRE you put in that field, because you can have false positives if you're not.