[npm] Error 'tunneling socket' while executing npm install

If you using gnome, and turned off the proxy at the network level, you also need to make sure you don't have proxy enabled in your terminal

? gconftool-2 -a /system/http_proxy  
 host = http://localhost/
 port = 2000
 use_http_proxy = false
 use_authentication = false
 authentication_password = 
 authentication_user = 
 ignore_hosts = [localhost,127.0.0.0/8]

You can drop it with

gconftool-2 -t string -s /system/http_proxy/host ""
gconftool-2 -u /system/http_proxy/port
gconftool-2 -u /system/http_proxy/host
unset http_proxy