It wasn't even criticism, constructive or otherwise.
An API has what at Microsoft they called "customers"; people who use it and expect defined results. L plunged ahead and changed the behavior without discussing the changes before or after, and he was unresponsive to questions.
I'M the one who is accustomed to working alone; but when working with others I take care to communicatee in great detail, I almost always write brief internal documents so people don't miss or forget details conveyed by voice.
L made critical breaking changes to this API and didn't even see fit to mention it. And no I had never been rude to him or given him any reason to resent me or see me as unapproachable.
He was infuriating to work with. His harsh and loud voice, his pointless screen-sharing. his illegible and poorly structured code, his caprice in making changes. And worst of all his refusal to communicate.
This API was my last new code on this project; I hung around a few weeks without pay to assist in the integration, and a good thing because we ran into some issues that weren't in the cryptographic documentation, all of which I fixed.