Irregardless is not a word. Period. I heard it THREE times yesterday. I usually only hear it about three time per month. I literally cringe every time I hear someone speak it. (It's surprisingly easy to type it, though. And to proofread it.) If you use this word, you owe it to yourself to stop.
Here's the funny part. When someone says "irregardless," the word they're actually looking for is "regardless." You see, "regardless" is a synonym for "notwithstanding." So saying "irregardless" would be like saying "notnotwithstanding." (By the way, "notnotwithstanding" isn't a word, either.)
The worst part is when I hear it on TV, especially the news. Newscasters are professional talkers and the only time I've ever heard them say "irregardless" is in one of their off-the-cuff moments. In other words, the teleprompter doesn't read "irregardless," the anchors themselves actually think that the word can be found between "irrefutable" and "irregular" in the English dictionary. (Go ahead. Look. It's not there.)
There is pretty much only one time that the word will actually make me laugh:
Do you know any adults with a very limited vocabulary? Sure you do. They say something like "defibulator" and you compliment them for saying a big word, even though it's actually "defibrillator." Or they'll say "carburetor," but you know they couldn't spell it if you asked. Then, that special someone will one day bust out the biggest, baddest word they know: Irregardless. This is where you laugh to yourself because their greatest vernacular feat is undeniably and unwittingly false.
That probably makes me sound like a big jerk, but I promise, it's all in good spirits. Irregardless is becoming more common, it seems, so I'm starting to get jaded to it. Don't get me started on "hisself," though . . .