1. Be a DK.
2. Find yourself an unfortunate PvP opponent (if you're level 110, your goal should be to hunt down them 100-103 lowbies)
3. Prepare for battle! Cast your Death Gate ability.
4. Kill your opponent ASAP (I managed to oneshot a level 103 boomkin with a single Marrowrend)
5. Click Death Gate to teleport to Acherus.
Once you're in Acherus, you'll get attacked by your own order hall guards. Beware though, they hit quite hard, so you might want to take the portal to Dalaran to escape.
Congratz, you're now being attacked by Kirin Tor guards! People around there watch you battle them and get confused. They're not that hard to kill, I easily tanked 4 of those with my 837 DK alt.
P.S. even though the guards belong to Kirin Tor faction, killing them doesn't affect your standing with Kirin Tor.