My son was bullied all through primary school he is now in secondary school year 7.
This isn't an excuse but just backstory so you understand why he reacted so badly...
He was being teased (where is the line between tease and bully?) and had some pencils stolen from him by some girls. he responded with a rape threat (to their mother).
We have punishment in hand. But how do we explain WHY this is so WRONG, so he understands why he is being punished so harshly.