Chef install isn't optimized yet for OS X 10.9 but there's a hacky way to get it installed.
First, download the install file at https://www.opscode.com/chef/install.sh
Then, edit the install.sh
file and change this part:
"10.6") platform_version="10.6" ;;
"10.7") platform_version="10.7" ;;
"10.8") platform_version="10.7" ;;