I just had this similar crash. I'm a newbie, trying to go thru the Ruby on Rails Tutorial. I just ran rails generate scaffold User name:string email:string and got a segmentation fault. This is on OS/X, same ruby version, and same json parser.
jerrys-mbp:demo_app jerryk$ rails generate scaffold User name:string email:string
/Users/jerryk/.rvm/gems/ruby-2.0.0-p353/gems/json-1.8.1/lib/json/ext/parser.bundle: [BUG] Segmentation fault
ruby 2.0.0p247 (2013-06-27 revision 41674) [universal.x86_64-darwin13]
Another occurance here. I'm trying to follow exercise 3 in section 3.5 of http://ruby.railstutorial.org/chapters/static-pages#sec-static_pages_exercises and get the same error on all commands after I tried to configure the Rails application with psql: "rake db:setup", "bundle exec rails s". Latest crash report, from "bundle exec rails s", is attached.
The database is up and "psql" manages to connect to it and execute commands on it.