It's in the Urban Dictionary, and the accepted definition puts it in the same boat as "Can't get no satisfaction":
Used by people who ignorantly mean to say regardless. According to webster, it is a word, but since the prefix "ir" and the suffx "less" both mean "not or with" they cancel each other out, so what you end up with is regard. When you use this to try to say you don't care about something, you end up saying that you do. Of course everyone knows what you mean to say and only a pompous,rude asshole will correct you.
/johnny