Originally Posted by Packrat

The approach taken by lexicographers when documenting a word's uses and limitations can be prescriptive or descriptive. The method used with irregardless is overwhelmingly prescriptive. Much of the criticism comes from the double negative pairing of the prefix (ir-) and suffix (-less), which stands in contrast to the negative polarity exhibited by most standard varieties of English. Critics also use the argument that irregardless is not – or should not be – a word at all, because it lacks the antecedents of a "bona fide nonstandard word."