GitHub User: ravage
Check your PATH (export PATH) in .zshrc and remove all references to .rvm within it. You should end up with something like this export PATH=/usr/local/bin:/usr/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/texbin
When installing oh-my-zsh it will look at your current PATH and fill your .zshrc with it, which also pulls .rvm environment. And you won't want that there since rvm should be handling it.