The ONE time you accidentally use the word "butt" instead of "bootie" while talking to your kids...
(as in, "Listen kid, when I said, "sit down" I meant on your bootie ... not on your head!")
... make sure it isn't while you're at the library.
Rest assured that those little ears that never seem to hear ANYTHING else you say ... well, they'll hear this... and it will amuse them to no end.
Next thing you know, the quiet tranquility of the library will be interrupted by the repetitious sing-song,
"butt butt butt buttbuttbuttbuttBUUUUTTTTTT!"