If you’re playing on a PvP server, there are certain areas where both factions can be found, but where it’s not allowed to hit anybody from the other faction.
In other words: No ganking of allies with your horde char.
Unless… There’s a smart WoW trick, you can do, if you want to make a fast in and out killing in neutral areas. (Even if you don’t have characters on a PvP realm, take a look at this cool video, you’ll laugh.)
You need a friend with a chopper or an other mount that can carry passengers.
The two of you create a group, and your friend (or yourself, if you’re the one with the cool mount) will not be allowed to hit anybody. He should stay on his mount, ready to ride, when you’re done.
Seek out a victim, jump off (only the passenger), hit, and jump in again, before the guards will have time to catch you.
Since your friend is already mounted, you’ll not get the “you’re in battle” message blocking you from mounting.
Take a look at this video, where two cool Chuppa Chicks do the gank’n’spank, hit’n’run tricks.