I used to have a(n abusive) boss who would deliberately include "per our conversation" in emails when there had been no such conversation, in order to cast blame for his shortcomings/lies on some else.

He would also do things like demand updates in reply-all messages with the heavy implication that he has been left out of the loop.

I started replying to those emails with "per our communication on [date]", referencing verifiable proof through emails that he was the one at fault for whatever issue he was trying to throw me or someone else under the bus for.

He stopped.