You can disallow certain words in comment posts by turning on the bad words filter via configuration maintenance and editing the bad words file which is badwords.php. The badwords array in that file looks like this:
$badword = array(
array("badword1","%@#*!"),
array("badword2","*****"),
array("badword3","bleep")
);
The word on the left will be replaced with the string of characters on the right. Change or delete the example entries and insert new entries for words you want to filter. All entries in the array except the last must be followed by a comma.