Find a confidante in the office, who will hit reply all and ask him to kindly take them off his list for these kinds of emails.  I bet there will be several who will send him a "me too" email and eventually he will have to quit doing it.   In addition, save every petty email, you may need it in the future.  This guy should not be trusted.  However, I agree with Wendy, you should take the high road.