I was on for just a quick mining run back in Vanilla, and my guild needed an OT for ZG. They brought me in, and I had no idea what was going on. To give you a better idea, I leveled as a prot warrior and didn't even tank in instances. THAT's how bad I was.
They brought me in, and I kept running in to "tank" things (I guess?), and all I knew was that they were supposed to be hitting me and I would get heals. So I did this for about 10 minutes, and I was getting blasted in guild chat. Then someone said, "He doesn't have vent - he doesn't know what to do - calm down." I asked what vent was, and there was a collective guild facepalm. When they told me, I rage faced at my computer and was like YOU CAN HEAR EACH OTHER TALKING!?
I've come a long way since then leading my own guild and raids in previous xpacs, but I still laugh and smile thinking of that moment.