https://www.reddit.com/r/antiwork/comments/ydnoew/coworker_freaked_out_on_me_for_a_joke/
Additional context in the comments of the original post.
Here’s the update. I got to work this morning and as soon as my boss saw me, he apologized for his brother’s behavior and promised to talk to him about it.
Then, just a few minutes ago, that coworker came in and apologized to me himself. We patched things up and I told him I understood.
Overall I’m very satisfied with how everything turned out.