Without at least letting me proof read it?? DP has submitted a complaint re some research conducted at dd's school. I was annoyed about the issue too, but he didn't tell me he'd submitted a formal complaint until after he'd put it in. Despite having a work colleague proof read it the letter he's submitted is full of grammatical mistakes and just reads like a rant.
He says he added my name because colleague told him it was better if it came from both of us. He doesn't think he's been unreasonable at all.
So
YABU - DP was just going what he thought was right
YANBU - DP shouldn't have sent it without checking with me first