No Ma'am

Nothing makes me bristle more than hearing someone call me, "ma'am." Upon hearing it directed at me, I always stop and think, 'Was s/he talking to me?' and then I walk away muttering, 'I'm no ma'am!'
I tend to find this word directed at me more at the grocery store. I guess management at Wegmans train their employees to be polite, right down to the cart boys. I had one say, 'Thanks and have a nice day, ma'am' when I returned the cart to the cart return. I just turned around and stalked to the car mouthing, 'Do I look like a ma'am cause I don't feel like a ma'am!'
I still get carded at bars - even college bars. For being 31, I think I can pass for low-mid 20s, at the very least. I understand that these cart boys are like 15-17 years old, but still, I'd rather they don't address me at all. You want me to have a nice day? Don't call me 'ma'am.'
I had another situation occur earlier this year when I was shopping in the Brass Plum section of Nordstrom. (For those of you that don't know, Brass Plum (BP) is Nordstrom's junior department.) I was actually having a string of good luck finding some really cute things in there for myself and so when I happened to be in Nordstrom, I'd venture down to BP and check things out. One day, one of the sales girls walked by me and said, "Are you finding everything okay, Ma'am?" Ugh. Okay - maybe I don't have the body of a 'juniors' girl (I've always hated odd number sizes anyways) but if you want my business, don't call me 'ma'am.' I can't remember if I left shortly after that cause I felt like the sales girl might've been asking after me as if I was looking for a gift for my niece or something. I don't venture down to BP very often anymore.
Who should be a ma'am, then? Maybe someone over 40 or someone that looks like they're over 40. I'm thinking June Cleaver.
So where does that leave the 30-somethings? Hmmm....to quote Britney Spears, 'I'm not a girl...not yet a wo-ma'am.' So maybe you just shouldn't address us at all - just tell us what you want and leave it at that. I think most of us would be much happier if you did - at least I know I would!
When I reach 40, we'll see how I feel about it then. In the meantime, no ma'ams for me.