My nephew had a bully years ago, my sister and her husband crying begged me not to get involved since they knew it was not going to end well.
Brother-law went and spoke to the Parents, they were a little less interested than he preferred, he than asked the father if he knew me, he replied yes and told him that i was his sons Uncle and we were very close.

I am no one incredibly important but the guy knew me from High School and also knew I was a bit of a Nut Job and could be Dangerous.
They never had an issue again.

My sister was pissed at me and I told her I never pursued the issue and left it alone, she did not believed me until her husband told her he dropped my name thinking the guy might have known me.