How can I completely remove Ruby + Rails + Gems?

If you're using Ubuntu Packages run sudo apt-get purge <packages>

So that should be something like:

sudo apt-get purge ruby rubygems

From the apt-get man page:

  purge
      purge is identical to remove except that packages are removed and purged (any configuration files are deleted too).

If you are using RVM why bother even uninstalling the system ruby?

I install both 1.8.7 and 1.9.2-rc via RVM.

After you have installed RVM you can set the RVM 1.8.7 to be your default ruby installation. Just don't install RVM as root.

For those wondering, https://rvm.io/ has the RVM install instructions.

Make sure you read the instructions on what packages you need to install for Ubuntu before installing 1.8.7 via RVM. If you don't install them you may have issues with some gems.

Using synaptic, you can remove the Ruby packages (select "completely remove" option). I guess this is the equivalent of the commandline: sudo apt-get purge

Now for the gems: they are not considered as packages. You will need to delete them manually (unless you want to use Ruby to do it, but since you say it's broken...)

By default, the Ruby gems are installed in your home folder, under the .gem folder. If you really want to get things clean, just delete ~/.gem, and it should be enough. When you reinstall Ruby and everything, the folder will get created again, and you will be good to go.