Gentoo Linux and Ruby are not working out well.
Some Gentoo Maintainers obviously think it's wise to have a lot of Ruby Gems in their own Portage tree or in the Portage overlay "ruby". Why would someone want a packaging-system on top of a packaging-system?
It gives dependency hell and not-up-to-date packages. I can't install ruby 1.9.2 decently by just "emerge ruby". What the heck? Ruby 1.9.x is out since ages. This got on my nerves - so deinstalled everything ruby from the gentoo system and used "RVM" instead.
Unlike Gentoo Portage concerning ruby, RVM just does what it says it will! Give it a try! It easily prevents every typical gentoo package problem with ruby.
https://rvm.beginrescueend.com/
So, installing RVM and ruby afterwards is as easy as:
bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)
cd ~/.rvm/bin
./rvm install ruby-1.9.2
Have fun
http://klumpp.net/blog/ am : Leichtgewichtige Alternative zu RVM und rbenv