Don't get me wrong, I am well aware that Merriam~Webster added it to the a Dictionary. What choice did they have? The word now flies out of more peoples mouths probably more so then the slang word "ain't" now of days, which was also added to the dictionary!
The proper word is "Regardless" no matter what the dictionary says, which technically, pay close attention to exactly what the dictionary 'does' say!
Irregardless defined:"Irregardless originated in dialectal American speech in the early 20th century. Its fairly widespread use in speech called it to the attention of usage commentators as early as 1927. The most frequently repeated remark about it is that “there is no such word.” There is such a word, however. It is still used primarily in speech, although it can be found from time to time in edited prose. Its reputation has not risen over the years, and it is still a long way from general acceptance. Use regardless instead."
My thoughts are as follows, if you want to look and sound professional, you won't use the word irregardless. Dress for success, strive for success, and speak, talk and think it, and you will get there. "Regardless" of what gets in your way!
Think before you speak, and always choose your words wisely. After all, they represent you.