Did you install rvm locally, or system wide? I have never had a real problem installing rails with rvm on 10.10, I just had to apt-get the required libs for ruby, and then everything else worked fine (with a normal rvm install).

I would try rvmsudo gem install rails, who knows...

Also remember, when you run the rvm install script or any of the following rvm commands, dont sudo it for a normal installation.