You can try Spam module.
It runs filters on posted content, for example using regexps.
Another way is to write a Rule that examines posted comments and deny them if certain words are found, but unfortunately this module is only available for Drupal 6.
And also you can write a validate function to the comment form, examine the content on submission and use form_set_error if you detect those words. To do this just implemente the hook_form_alter (or the hook form alter with form id), add your valditation function:
$form['#validate'] = 'you_custom_validate_function';