Synopsis
So sad to see you go.
sudo npm uninstall npm -g
Or, if that fails, get the npm source code, and do:
More Severe Uninstalling
Usually, the above instructions are sufficient. That will remove npm, but leave behind anything you've installed.
If that doesn't work, or if you require more drastic measures, continue reading.
Note that this is only necessary for globally-installed packages. Local installs are completely contained within a project's node_modules folder. Delete that folder, and everything is gone less a package's install script is particularly ill-behaved).
This assumes that you installed node and npm in the default place. If you configured node with a different --prefix, or installed npm with a different prefix setting, then adjust the paths accordingly, replacing /usr/local with your install prefix.
To remove everything npm-related manually:
rm -rf /usr/local/{lib/node{,/.npm,_modules},bin,share/man}/npm*
If you installed things with npm, then your best bet is to uninstall them with npm first, and then install them again once you have a proper install. This can help find any symlinks that are lying around:
ls -laF /usr/local/{lib/node{,/.npm},bin,share/man} | grep npm
Prior to version 0.3, npm used shim files for executables and node modules. To track those down, you can do the following:
find /usr/local/{lib/node,bin} -exec grep -l npm \{\} \; ;
See also