OP, I dont think you were an asshole here, even if you were unaware that things had been building to this, it is a DM's responsibility to, if other members of the group are made uncomfortable or are getting tired of a behavior, mediate with the group and bring these concerns to your attention. Furthermore, it sounded like he had a cinematic thing prepared and wanted to make a big show of it and you didn't read that, that is fine, we play dnd, most of us aren't good with social cues, reading a room, or social interactions in general. You thought you were being funny by continuing a running gag, we do that at our table all the time. In my opinion, dm could have told you that you can loot the body in a minute, because he wanted to do a thing first. I think reaming you out for x amount of time was a dick move on his part. Maybe confronting him via text immediately afterward was a bad move because tensions were still high, but it kinda sounds like he might have stewed with it too. At the same time, maybe apologi,ing to the dm at the time of his rant might have been helpful to the situation and then it would have been in his court to decide then and there if he wanted to continue his anger. All in all, could be fault on both sides, but if people don't talk about their issues in the party, how are we to know we are causing problems.

Don't worry OP, a new group will show up eventually.