Noobish Question
 

What does it mean when a mob can enrage/rampage?

Sorry to trouble you salt dogs with such a question ;)

Enrage- if you are in front of the mob and attacking him he hits you back, sucka!
Rampage- if your "on rampage" as in person with second most agro IN mobs melee range, you will get attacked AS WELL AS the tank.

Rampage is the first living character to get on the mobs hate list within melee distance also gets attacked. Unless that person is tanking in which case it is the second.

Just to elaborate more on Enrage.. Melee attacking from anywhere that is 180 degrees on the front side of the mob. Basically reflecting the melee attack back to it's source. I say 'damage reflection' but the attack is being riposte. As the mob takes no damage from the attack you'll be hurting yourself on top of any damage the mob does to you if you're the mob's target. Mobs that enrage tend to do so at low health 10% or less.

This is just one reason why you'll often see the player tank alone in front of the mob. While the other melee attacks are somewhere 180 degrees behind the mob. When the mob enrages the tank turns off autoattack until enrage is over. Meanwhile the melee attackers behind the enraged mob can continue attacking without killing themselves.

It isn't second highest on the list. Its determined by the order on which you got on the list in the first place, regardless of your current hate (unless you drop off altogether, obviously).

To be more specific on enrage -
If you are a highly hasted dual wielding melee, for instance, you will take a hit for each swing you make, but at the mob's DPS value, so you will be getting hit for multiple hundreds a pop very fast. It's equivalent to having someone max haste a dangerous mob and you just going and standing in front of it. You don't last long.

It means the thing is almost dead.

Good point, thanks.