Take it to the principal -- and the School Board if necessary. Also, make it clear that your child will leave the classroom if he brings it up again.
Until I mentioned the principal last year he was going on about it all the time and it was upsetting to my daughter.
Once I mentioned taking it to the principal he shut up.
New year...now my son has him...we'll see if he starts running his mouth again.
If he does I'm going to the school board.