The generic-versus-brand-name thing is what really used to hack my mother off, because she is housebound and has carers who do her shopping.
On more than one occasion she has asked for something specific, clarified that she does actually want that, and they would come back with something else. "Oh, I know you said you wanted Sudafed, but Otrivine was cheaper!" (Yeah, and it doesn't work!) "Oh, I know you wanted Mellow Birds coffee, but I got this Asda brand instead." (Yuck!) "I know you said two bags of potatoes, but you'll only need one." (My daughter is coming down for Christmas with her husband - I said TWO because I will need TWO!) Drove her nuts.
Fortunately they seem to have finally got the message, possibly after one of them ended up lumbered with a bottle of a horribly sweet alcohol that Mum didn't want. She had asked for a box of chocolate liqueurs, the carer wrote it down wrong and came back with a bottle of chocolate liqueur. I gather it was vile.
Many moons ago I worked in a grocery store. At the time I often did the shopping for those that needed it done, usually either home bound or those with vision problems/blind. I was actually one of the mid rung managers, so not really part of my job per se, but so many people specifically asked for me because I got them exactly what they asked for or the nearest equivalent if something was not available (calling to clarify anything that I didn't understand or to okay a substitute prior to actually putting it with their order).
Many places and other people just chucked whatever, ignored name brand request, and subbed whatever they felt like. The one that stands out was a lady who wanted X amount of vanilla beans and someone got her a big bottle of imitation vanilla extract.
I personally walked over her vanilla beans as she lived in the senior complex across the street and explained to the person doing the shopping how those were not remotely the same. His response was along the lines of he didn't know the difference so he picked up what his mother usually bought.
My name brand vs generic peeve is with tissues. When I'm sick and snotty I want Puffs with lotion and no other kind will do. My nose gets all red, sore, crusty, flaky and peels otherwise. I don't mean I want Kleenex, I don't give a dingdangity what is on sale, I want exactly what I wrote down. Same thing with pain relievers, the only OTC thing I can use is Tylenol/acetaminophen (this is doctor ordered. Years ago a Friend went to the store for me while I was sick. I wrote out a very detailed list and specifically stated on the list and to them in person that it was very important not to stray or substitute products due to allergies and doctor restrictions on drugs. I had to take back the whole order with 103 fever because there was not a single thing I could use in it. They picked up Aleve (I am not allowed to take NSAIDS because of bleeding issues), soup that the primary ingredient I can't eat, Sudefed that sky rockets my blood pressure, generic brand tissues, and the list went on. I was not the least bit happy about the whole hot mess.