The shocker? IRREGARDLESS is the improper usage of REGARDLESS. I know. It surprised me too, because so many people say it. In the past, I've said it myself.
The word is REGARDLESS. IRREGARDLESS is a double negative, and the "non-standard" use of REGARDLESS. It's improper all around and makes English teachers and editors cringe.
Example of the two words used properly: Irregardless is an incorrect word, regardless of your desire to use it.
Tuck that in the grammar slot of your brain, so you don't upset the grammar goblin. Never use irregardless again. You'll look so smart.
Tell everyone you heard it here first. Regardless of whether you did or not.
Then, I'll look real smart.