A lobotomy obviously.
The complete lack of desire to engage in any face-to-face interaction. Maybe even the ability to dissappear at will.
Guess what sweety, I came into your store today, ready to buy. Something quite expensive actually (do sales girls still work on commission, or is that just Pretty Woman?). I was the only one on the store but hey, maybe you didn't see me, what with your head stuck so far up your ass.
But I saw you. I saw you texting, fiddling about with your earring (they're not that complicated darling... the pointy bit goes through the hole) and wandering off in the opposite direction every time I tried to catch your eye. Trust me, you were one anger-management lesson away from being crash-tackled into a change room and duct-taped to that bloody register. Don't ask me where your phone ends up in this scenario, you, and your proctologist, won't like it.
So you had to work on a Sunday. Boo Hoo You. I'm sure you'd much rather be sipping lattes with your mates, getting your fake-tan done or finding out the name of last nights random shag (yes, you look the type). But tough shit, you're at work. Or maybe, given it's a small boutique (which I'm sorely tempted to name, but can't seem to remember) it's actually your store, in which case, it would be in your best interest to suck it up, put a smile on that surly dial of yours and wring out some actual service from your cold, hard self before someone not quite as Zen as me reaches for the duct-tape.