I've never been gkicked before, but I've been demoted from a raid team. This was back in WotLK during heroic Lich King progress. I think the main reason for my demotion was that I hadn't figured out how to maximise my camera distance on Sindragosa, so I often died to the massive AoE damage she did where you had to run out in a straight line. I felt like a total moron once I figured it out, but the damage was done. I was that moron who constantly died on Sindragosa, so I was demoted. It was a top 100 guild, so yeah. Made sense for them not to take someone like me to heroic Lich King.

I was actually really salty about it at the time, so I ragequit the guild and flamed them in trade chat. Then I joined a different guild and we progressed on heroic Lich King and killed it as server 2nd. So it wasn't all bad. A couple of weeks after ragequitting, I apologised to the original guild for my immature reaction and even rejoined them a couple of expansions later (by then I was a bit better and I had max camera distance!). But I handled it in a pretty childish way, haha.