I just wanna make a contribution to your self esteem - the fact that you even posted in here asking for help leads me to believe that you're not gonna be a derpy tank.
Even if you get into LFR and wipe the raid (which I very much doubt will happen) your stats will go up and you can just try again. People in LFR are doing the same thing you are. Even if they (probably a hunter, lol) start throwing some abuse at you in /i, just make it clear that you're gonna learn from your mistake and kindly tell them to kiss your booty.
LFR will not only get your gear raid ready, but it'll give you experi
