No, everyone doesn't 'know what it means', not without additional mental parsing. Myself, among many others, read it first as a double-negative, then have to double-take it and reinterpret it. Irrespective, irreducable, irrecoverable, irreconcilable, irrelevant, irreligious, irrefutable - irregardless stands out like a sore thumb.

Or should I say 'irreinterpret it'? After all, you would 'know what I meant' if I wrote that.

Ambiguity is fine if you're writing for poetic effect, but if you're trying to get a point across, it should be minimised.

Wait, are you really sYing that when you see "irregardless" that your first response is not "that's an error and they mean regardless[1]" but "they mean regardless but negated so regard but that doesn't make sense so they actually mean regardless"?

[1] why not irregard instead of regardless?

"that's an error and they mean regardless" = "additional mental parsing"

Yet astonishingly you are one of the people who knew what it meant.

Also, most English dialects don't strictly follow double-negation rules. I know this drives non-native speakers crazy, but you'll get over it with enough practice.

I think you missed my point - perhaps you should irreinterpret my comment.

It stands out because "regardless" and "irregardless" are adverbs, while the others you listed are all adjectives.

And it does fit the pattern of negating the root morpheme.

Everybody knows that it means not (not in regard).