Mommy, What is a Pagina?

Did my 3 year old just say what I think he said?  Yes, yes he did.  Apparently my three year old has learned a few words from his 6 year old brother and friends.  When he first said "Pagina" I corrected him and told him it was "Vagina".  He corrected me and told me I was wrong.  So we will go with it.  This is a tricky one.  Pagina is not a bad word, but how do you teach the difference to a three year old between how this word should be used and how it should not?  Right now, I am just trying to get him to not say it.  This has been a rather tough task.  Here are my top three favorite situations in which he has used this word:

Going to bed: Mommy, what is a pagina?  What is a butthole?

My reaction: Laughing (I was totally taken off guard and I could not help myself)

Walking through my Orthopedic doctor's office with an extremely loud voice: "Mommy, girls have a pagina and boys and girls have a butthole"

My reaction: Running out of that office with him and his sister as fast as I could.

Eating dinner with his brother and friends. He gets mad at them and says "You are paginas"

My reaction: This was done under the context of being mean so he was sent to timeout and warned that he is not to call someone this again or there will be soap in the mouth (seemed to work for my parents)

I am now currently on "pagina patrol", hoping that I do not hear this again.  In addition to pagina and butthole, here are some other fun words that continue to come out both of my boys mouth that I am trying to get a handle on: underpants, underwear, boobies, poo, pee.  

Raising boys is definitely an experience.....