Who is the Tank in my Party?

Assuming everyone's level is equal, tanking responsibility goes in the following order:

1. Warrior
2. Paladin
3. Warlock's VW (VoidWalker)
4. Druid's Bear/Dire Bear form
   
5. Hunter's Pet
6. Hunter
   
7. Shaman
8. Rogue
9. Warlock

Players who should never tank:

1. Primary healer (regardless of class)
   
2. Priest
3. Mage