Grammar Nazi enters the room.

I believe Corino is right. "Regardless" is already the contrast of "regard" so irregardless becomes the double negative that some people might consider acceptable but an old school English enthusiast usually would not. Originally it was not acceptable as it's an unnecessary double negative that almost NEVER means the thing people think it does when they use it in a sentence (because they're thinking it means regardless)... Even if we agreed it's an acceptable word, it gets used wrong 99% of the time if we accept it because the way most people use it would be similar to claiming "irresponsible" means the same thing as "responsible."

Another point I always enjoy hearing about is how someone can claim "conversate" is acceptable when originally it was not and only should be stated as "converse." Conversate sounds better in rap songs though... "conversate for a few, cuz in a few, we gun do, what we came to do... ain't that right boo? ...Truuuue" - Anyone know the song?

Grammar Nazi exits with a banana in hand, regardless of whether you like watching bananas get eaten by Sgt. Doakes.