In the Installing RVM->Installation page/section, the --branch option parameters are defines as:
\curl -sSL https://get.rvm.io | bash -s -- --branch [owner/][repo]
The repo parameter is incorrectly defined; it's actually the branch. This confusing, because it implies that differently named forks are supported (e.g. 64kramsystem/rvm-dev, while they actually aren't.
A fixing PR will be submitted shortly.