NOW I understand.
For the last few years, I've been really confused about why, when I ask for skim milk at a coffee bar or order a skim latte, I will sometimes get blank stares in return. When this exchange involved a Starbucks and the barista would simply repeat back to me my order with the term "nonfat" instead of skim," I just assumed that it was the same passive-aggressive tendency that makes them repeat "tall" when I (very passive-aggressively myself) order a "small." But no!
THEY DON'T KNOW WHAT SKIM MILK IS.
"sometimes people ask for skim or skinny lattes and i have to explain to the newbies that skim/skinny means nonfat."
And to all the Starbucks baristas I've ever met: I'm sorry I keep insisting on ordering "smalls" instead of "talls." I just really, really don't like the Starbucks branding. And also, if I ask for a "tall," I feel like I'm participating in duping myself into thinking that I'm somehow getting more coffee than I really am. But I do realize that this sort of thing must get annoying for you.