I am in the deepest level of RVM Hell (a sublevel of the deepest level of Xcode Hell, which itself is the deepest level of Apple Hell (flowchart to follow)). This is how I ended up there, and what I was told along the way.
# via fresh rvm installation
rvm pkg install zlib
set -x
CC=/usr/bin/gcc-4.2 rvm --trace reinstall 1.9.3 --with-gcc=/usr/bin/gcc-4.2 --with-zlib-dir=$rvm_path/usr
set +x