Had some problems in a new Ruby 2.1.0 install + Ruby 2.0.0-p353 with the latest BSON gem (2.1.0)
[1] pry(main)> require 'bson' NameError: uninitialized constant DateTime from /usr/local/opt/rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/bson-2.1.0/lib/bson/date_time.rb:64:in `<module:BSON>' [2] pry(main)>