Tonight I was going to give the mean stack a try on my MacBook Pro, when I ran into these kind of problems trying to install some packages with npm.

npm http GET https://registry.npmjs.org/npm
npm http GET https://registry.npmjs.org/npm
npm http GET https://registry.npmjs.org/npm
npm ERR! Error: SELF_SIGNED_CERT_IN_CHAIN
npm ERR!     at SecurePair.<anonymous> (tls.js:1356:32)
npm ERR!     at SecurePair.EventEmitter.emit (events.js:92:17)
npm ERR!     at SecurePair.maybeInitFinished (tls.js:968:10)
npm ERR!     at CleartextStream.read [as _read] (tls.js:462:15)
npm ERR!     at CleartextStream.Readable.read (_stream_readable.js:320:10)
npm ERR!     at EncryptedStream.write [as _write] (tls.js:366:25)
npm ERR!     at doWrite (_stream_writable.js:221:10)
npm ERR!     at writeOrBuffer (_stream_writable.js:211:5)
npm ERR!     at EncryptedStream.Writable.write (_stream_writable.js:180:11)
npm ERR!     at write (_stream_readable.js:583:24)
npm ERR! If you need help, you may report this log at:
npm ERR!     <http://github.com/isaacs/npm/issues>
npm ERR! or email it to:
npm ERR!     <npm-@googlegroups.com>

When I checked my version with npm --version it told me I had 1.3.11 which had a problem with self signed certificates, so I tried to update my npm installer with npm update npm -g. Too bad! That got me the same error.

So after some Googling and reading other peoples problems I came to the following solution:
sudo npm update npm -g --registry http://registry.npmjs.eu

Apparantly switching to another npm-registry was enough to fix this nasty problem. I now have version 1.4.4 and my packages install great again!