I haven't had anyone get nasty, most are just confused. As am I. As is everyone else. And pissed off by how stupidly specific the items allowed are (even when it costs so much more than if they'd be a bit more general with the allowances). When I'm helping guests on the floor I send 4-5 different versions of grocery items up with them in the hopes that one will work, as even items that look like they should be allowed, based on the check, come up as not-allowed.
And don't get me started on requiring them to buy 9 tiny cans of formula which is so fucking much more expensive and less likely to be in stock in sufficient quantities than if they just gave a max allowed quantity or dollar value for said formula.