I won't name the subreddit, because it essentially names the moderator involved, but I answered a question regarding website performance on a popular developer subreddit. Someone responded back by saying that I was clearly a terrible developer because I said that squeezing performance out of a personal site wasn't essential. I told that person, quite bluntly, not to be a dick, and I got permabanned with the message "no, you're a dick".
I protested to one of the mods, not necessarily for my ban to be rescinded, but for that mod to stop being a dick to people. His comment history showed a pattern of that behaviour, and (most likely) a pattern of bans. The other mod unbanned me, and I left it at that.
Weirdly, the only subreddits I've ever had problems are the larger ones. I post regularly on /r/Games and /r/bjj, and both are moderated brilliantly.