The ExtraLife community has a great section for WoW/the Instance – and there was a post there with the Question of the Week (QotW) – What noobish moments are you willing to share with us?
A long time ago I remember realising* that I had my rotations and methods of healing as a Paladin all the wrong way round. No bloody wonder that my mana bar always ran out, my raid group seemed to die a lot, and that I chugged potions like they were going out of style.
* Being told by the GM and resident Paladin class guru that I was killing people by being such a noob. Fark, what a bad day for the ego.