I don't know if it was exactly traumatizing, but, churches. When I was like, somewhere between 9 and 12 I had to spend a significant amount of time once a week in a room with a ton of my peers without my mom there for the first time. (I was homeschooled.) They were unruly and loud, and I hated most of them. I don't think it caused my social anxiety, but it definitely made it worse. The once I talked to one of the adults about my issues, she said the solution was to go make friends, one of the many indecents that left me bitter towards and mistrustful of all staff at all churches because I didn't feel like they would listen. The pastor was also super homophobic.
Different church time: I was doing VBS one year at a church in a different state than I lived in at the time, and in one of the games they had us play when a signal happened the kids had to run to get into groups to form their bodies into a shape that was called out by one of the adults, and when the signal was done again whoever wasn't in a shape was out. Predictably, everyone was getting into groups with their friends, only I didn't know any of the other kids. For some reason one of the adults though it would make me feel better if she put me back in the game, so I remember getting out in every single round (we did like 6) because no one wanted to take a chance by teaming up with the new kid (which my brain for some reason interpreted as no one liking me) and trying not to let anyone notice it bothered me because a. I didn't want to be noticed too much: everyone else in the group was happy, so I had to be happy. and b. I didn't want to look ungrateful: I was being given special treatment by an adult, so I had to appreciate it.
Generic church troubles: I almost always knew the answers to a lot more Bible question, or had more in-depth versions of the answers, than my peers, so I ended up a bit of a teachers pet, would be nice except for the fact I secretly hated both of the teachers in question. None of my peers took my concerns seriously, so I ended up a. Deciding to o look out for only myself, let them suffer since the never listened. and b. Being very paranoid (it didn't cause the paranoia, just highten it), clearly no one else took any of my concerns seriously, so I had to be extra observant and take them all seriously. I only ever had more than 1 friend at the same time once, and it only lasted like 2 weeks.