Wear your T-4/T-5 gear, plus any other "defence+spell damage" pieces. Don't gimp your defensive gear too much - you should be wearing MT gear so the healers don't say you're squishy.
If the raid leader won't let you tank it, say you're there to DPS.
If you have a hunter friend, get him to MD you every cooldown. Get grouped with a Shadow Priest and a shaman, and have the shaman drop "Wrath of Air", IE: you want to be in one of the DPS caster groups, NOT the MT group. Bless Sanctuary, Retribution Aura.
Judge Crusader, pop wings, and do you max threat rotation. Use a mana pot as soon as you're down 3k mana. Once you have threat (first knockback, most likely, maybe earlier) get max rank Holy Shield in your rotation.
Proceed to hold aggro twice as well as any other tank.
Remember to spam Hammer of Wrath as soon as he hits 19% so the executing warriors don't out-threat you for the last minute or so.
At the end of the fight, say "So, how was the tanking?"
If not promoted to part of the MT team on the spot, the G-quit and get a real guild.
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