Ooh, I've got a doozy from the last time I went to petco. I usually buy my rats from a local place, but they were closed, so I swung by petco (or was it petsmart? One of the two). I opened the freezer and popped open a box of rats to see how big they were. An employee took this as a sign of me being confused, and after asking what kind of snake I had and how big it was she said, "With snakes like that you need to feed them a mouse that isn't any bigger than its head."
LUCKILY, her coworker corrected her... by saying, "No, I'm pretty sure the mouse can't be any bigger than the space between their eyes."
...I just thanked them, told them I know what I need to be feeding and went on my way.