The warrior class has a skill used in defensive stance, called "Intervene". This skill is used when a party/raid member gets aggro, so the warrior can "charge" the partymember and take the damage meant for the charged target. However, on certain EMU server this ability doesn't work as it suppose to. Instead of taking the damage of your target, you will start to hit him.
So, if you got ppl you dont like in your party or raid, simply go into Defensive stance and intervene him, and kick his ass!