Here's a good one!
My Grandmother IL kept asking if the baby needed some formula, and I said "no, she doesn't drink formula" (also she wasn't hungry). GMIL was so horrified she kept asking "She really doesn't drink formula?" "are you sure she doesn't need some formula?" and so on over and over, and I kept saying, "No, she doesn't drink formula!" I thought it was silly but I didn't understand why she was so upset until finally GMIL said "Well then , what does she drink!?" She didn't know a baby could drink anything other than formula! When I explained that "she drinks breast milk" GMIL was even more horrified, "You mean she just drinks cow's milk!!?" This woman has 4 kids and a ton grand kids and great grand kids, and she honestly had no idea what "breast milk" was!