There are plenty of times where people can be inconsiderate, selfish or mean, but once in a while you come across someone purely evil. The type of person that should be locked away from society or squished under a large rock.
I've just started leveling my mage with a friend in outlands starting with hellfire peninsula. We both grabbed the one PVP quest to cap the three bases in the middle and figured we'd do it when we happened to go by.
Well we tried one night and a level 80 priest was there waiting to kill us low-level types. We go down in one or two hits. Corpse run back and my friend gets away, I don't. I can totally understand and forgive someone attacking a flagged player in a PVP location without looking at their level, once. If you go out of your way to kill them a second time knowing you won't get anything out of it then you are just a jerk. It was late and we gave up for the evening.
The next time we go and cap the first one only to be steamrolled seconds later by a hunter and paladin who then proceed to camp our corpses. I was about to give up when I decided to flip to my main, get some help and trounce the punks. We did.
Capped the other two without any competition and headed back to honor hold to turn in our quest. This is when asshattery turns to evil and the paladin, Renderence of Perenolde, swoops in on a flying mount and decided to one shot our low-level alts in town.
Funny how he didn't want to attack our mains of his own level, but had no problem attacking characters over 15 levels lower.
It is one thing to attack someone in a PVP area who is flagged, no matter the level or reason, since if they are in the area and flagged they are sort of consenting to be killed. Even still it isn't nice to gank lower level toons.
A line gets crossed though when you follow someone obviously no longer interested in PVP and ambush them. In a grossly unfair fight no less where you have no chance of losing.
These types of people go to a special hell with toy trains and mohawk grenades.