- shouted at you in a meeting claiming that your opinions are invalid and that he didn't need to explain matters to you.
- being abrasive.
- blew up a PR review ("insane set of Github comments")
While I empathize with you and understand that such behavior shouldn't be normalized, it remains murky which of these are performance related. (What happened to the in-mem sql DB thing, what was his rationale for commenting in the PR review?)
Pardon me, but this reads like a one-sided take of the events that transpired.
I guess what I'm trying to say is that arguments happens and it's important to understand the rationale behind the friction rather than determining the eventual loser as the one being in the wrong; for the loser could be the one wronged.