I used this expression for about the first 25 years of my life. Of course it says the opposite of what it means, but it seemed to me that (1) all New Yorkers used this expression, and (2) we all meant it ironically.

I had a girlfriend after college who reacted like the woman in this comic strip. It drove her crazy.

What's more, she couldn't believe that I of all people — someone who was especially persnickety about logical and linguistic consistency — would use such an ignorant expression. I ignored her. I owe her an apology about that, I suppose. I experienced our difference as dueling regionalisms. (She was from Virginia.)

A couple years later, when I started reading books on linguistic nitpicking, I finally realized I'd been giving my fellow New Yorkers too much credit. Apparently "less" is mistakenly read as a negative, so "not … less" reads as a double negative, when it isn't.

But I must confess that I could still care less.