I tried to install cocoapods (http://cocoapods.org/) on my OSX Mountain Lion.
moshe-mbp:~ moshem$ gem install cocoapods ERROR: Could not find a valid gem
Current release of rvm does a lot better job handling this things, run:
rvm get head rvm reload rvm autolibs enable rvm reinstall 1.9.3 --disable-binary
Make sure to follow any displayed instructions - it's all there to help you.