This occurred with my parents when they were in Canada. They were shopping for clothes for me (I stayed home) and when they were approaching the cashier they were discussing whether or not they will fit me. They had gotten me a couple of miniskirts and a baby doll shirt (that's what they're called?) Now, I would think my mom would know my size best, but my dad kept arguing they were too small. My dad mentioned that I was about the cashier's size, but my mom just said "no, she's smaller," in no way insulting. The cashier overheard all this and I guess took it the wrong way and got all snappy with her. She snatched the clothes from her hand and went, "Yeah, well. These are out of style anyways" in a snotty tone. My mom responded with, "It doesn't matter. She looks good in these clothes."
sidenote : I'm a really small person, so apparently the cashier couldn't have been much bigger than me for my dad to mistake our sizes. My mom said that she was maybe a size bigger than me, so oh my god. Good job getting offended that you're not the skinniest person in the world.
I just think that cashiers should leave personal opinions to themselves unless asked otherwise and not get so easily offended. It's not like my mom called her fat.