So we are completely burned out with this project that had a fucking generic contract and my boss never had the balls (and never will) to say no to the client's endless requests and changes...

We are about to deliver it once and for all and they complain about one thing that I have already agreed to my boss that we would not do...
We tell the client that it is the case...

They email everyone involved in the project with a high level of drama on it...

I ask my boss, who is on vacation, on directions as to "how" I should tell them the fuck off...

My boss answer: I'm making a script to solve this issue and to avoid further trouble with it...

Ooo you stupid motherfucker! Can't you see you only bring more trouble with that attitude?