What Does that Mean Mommy?

Yesterday my wife had to pickup Random Girl from school early to take her to get a tire changed on the minivan.  She wouldn't be home in time for the bus so it was a necessary evil.  On the way to the tire store, Random Girl asked Mom what "bitch" meant.  What, WHAT?  Now, we refrain as much as possible from using foul language in front of our children.  The occasional explicative may escape, but usually on the milder side.  So, the conversation began that it was a female dog, but that some people use it as a derogatory word to describe people and that it was not nice and should never be used.  Apparently it's the favorite word of one of the little boys in the class.  The same little boy that spends his days in time out and ISST.  What a person I want rubbing off on my child.  So, the word was explained and she was cool with the not using it part.  She just needed to know.  What to do?  Should I talk to the teacher about the words this little boy is using or not?  Will it matter?  Oh, what a day to be a dad.