Heres my rules:
1) If someone steals my kill, but its not totally dead, ill steal it back.
2) If the enemy is near me, shooting near me, or goes into my crosshair, i fire
3) If the dweeb does take the kill, no apology, nothing, i will steal from him, per plane stolen from me.
4) If the dweeb is in trouble, i will not help, and kill the enemies killing him only once he is dead