Cashiers who are too nosy about what it is you're buying. I buy a doll or a stuffed animal and they ask "Who is this for?", and I get embarrassed because I have to answer "me". Or I buy craft supplies and fabric and they ask me what I'm planning to make with it.
And these days you can't just pay for your things and go, they ask you all kinds of annoying questions like do you have their store's credit card, do you want their store's credit card, what's your phone number, what's email address (I almost never give it to them because I don't want a ton of junk mail), would you like to donate to whatever, would you would you would you AUUUGGH!!