I've rage quit a group exactly once. It was a Darkhold run, with a DRK tank who admitted early on to being new to the dungeon. THAT wasn't what made me leave, though; it was how rude the healer and other dps started getting with him after he told us that he was new. They acted like not having run Darkhold to death by that point was a mortal sin since most players use that dungeon's first room as a leveling crutch, but they ignored the fact that Darkhold is an OPTIONAL dungeon, and that there are plenty of other ways to hit 50 and break into HW content (I ran Darkhold exactly once before reaching 50 the first time myself). Their attitudes were so poor that I just got fed up and left.