Irregardless, I'd Use It Sparingly

Few words in the English language prompt as much debate as 'irregardless.'

An evident mash-up of  'irrespective' and 'regardless,' the word affects some readers like sandpaper on a sunburn. Because of these strong feelings, I'd recommend against using it. 'Regardless' will do the same work, without the stigma.

An exception: If you have a character you want the reader to view as pompous, you might want to slip an 'irregardless' or two into his dialogue.

Is it a word? Is it not a word?

The Merriam-Webster Online Dictionary includes it as a nonstandard variant for 'regardless.' You can see it in all its glory here.