Rabble Rabble Rabble (Season 2)

You need 20+ people to be in queue for the arena before the portal spawns, I got it by making a raid group with 20 people queueing at the same time and the portal spawned right after we all queued.

[npc=68764] casts a portal to Orgrimmar, He's in the southwest corner of Bizmo's Brawlpub. He doesn't do this very often; I've only seen it happen once in the past 2 days, and I've spent quite a bit of time in the Brawlpub. He cast it at 2:42 server time on Bronzebeard-US. Once you take the portal, you get ported outside the gates of Orgrimmar, and you do not get flagged. I just teleported back to Stormwind with no issue.

He yells things like:
"I've made a portal to Orgrimmar. Who wants to kick some Horde butt?"
"This place is packed to the rafters with Alliance all-stars! Let's go tear apart Orgrimmar!"
"You folks want violence and bloodshed? Let's go take it to the Horde!"
"Did someone order a portal to Orgrimmar? No? TOO BAD!"
"Orgrimmar portal open, Brawl fans! Tell 'em Bubbles sent ya"

Portal seems to last about 5 minutes.

Willard is located in Bizmo's Brawlpub in the back corner opposite the entrance. (34,78)