Metaphysical Waitresses

Whilst on a day off I went to my local convenience store, which is good, because what's the point of a convenience store if its not local.  But I digress.

I picked up the things I needed and made my way to the till.  There was a lady in front of me, and the woman serving her seemed very friendly.  For whatever reason, her attitude seemed to change the moment I got to the head of the queue.  Don't ask me why but I felt as though I'd done something.  I was polite towards her but unlike the customer before me I did not receive any of this woman's friendly customer service (is it still customer service if they treat you like shit?)
With the items placed at the till side, ready to be swiped across the scanner, she looked me up and down.  So intently in fact that I could feel her eyes burning into me.  Like the customer before she asked me if I wanted a bag - not 'would you like a bag?' or 'Do you need a bag?' but 'want a bag?' As there were far too many items for me to carry without the aid of one I thought that was obvious.  What was she expecting, that I'd magically keep everything floating in mid air, under some sort of magic spell?  Maybe she thinks all men that wear glasses are called Harry Potter.
And when she did produce a bag from under the till it looked like it had been through the mill a bit.  Mangle more like, considering the state of it. At this stage I really couldn't be bothered to challenge her, so allowed her to continue.  Unlike the way she handled the previous customer's items she just threw mine into the bag. Not literally, she did at least notice that some items were bottled.  But did she pack the items into the bag as you'd expect, in a certain order, making sure everything was tidy, thus making it easy to carry?  Put simply, NO!
She finished packing the bag, and before shoving the change into my hand (rather than lay it on a bed of roses and then handing to me, which I often find in other shops), and without giving me a chance to pick the bag up she shouted NEXT!
For all I know, she may have been having a bad day and the lady in front of me was a friend who'd come in to cheer her up.  Surely if that was the case why did she go back to being miserable within a few moments of my arrival to the till?  Could there be something about me I just don't know about?  Maybe I did something in a previous life and a  metaphysical signpost hangs above me.