Edit: Sorry, Martha! Definitely did not pick up on the sarcasm. My bad!!
"In 5th grade most kids shouldn't know what a booby is"?! Really? In 5th grade nothing is funnier than boobies, butts, farts, poop, and burps! Every 5th grader probably knows what boobies are because they most likely have moms who have them! And some of the girls are most likely developing them!
It was definitely an "oops" moment - but based on the quality of the substitute teachers I had in school, I wouldn't make a big fuss about it if my child came home and told me that.
BTW - I'm not suggesting you're of the same quality as the substitutes I endured, just going back to my childhood as a reference!