Considering that under the EULA for most MMOs, and WoW in particular, you've agreed to not engage in vulgar or offensive behavior, it's a pretty clear cut no no that you've agreed not to get your epic mount on in Goldshire.
That being said, there's nothing to keep you from sending tells back and forth to your heart's twisted little desire, or even creating your own guild for nothing but people that want to do that, and everyone replaying the Battle of Mount Hyjal, after deciding who gets to play Hyjal.
On the other hand, it is very easy to just /ignore people, or just report them for spam if you don't want to clutter up your ignore list. You can even just turn off the display of local channels, for that matter. However, the EULA is on the side of the folks who don't want to have to wade through that. It would be different if we were talking about folks who were just spammy, but clean RPers, but this crosses into a clear violation of what's acceptable under the rules of the game.
So, you know, don't just get a room, because we can still hear you down here. Take it to tells, thanks.