Well, well, have to admit that I'm not that smart. Just like the old Chinese proverb: 智者千虑，必有一失；愚者千虑，必有一得 - well I'm just kidding. Anyway, *NEVER* use 'sudo vim /etc/sudoers', use visudo, because it performs basic syntax checking to prevent the file from corrupted. However, if you're reading this post, you may also want to know how to undo the stupidity. Now here goes the shot:

1. Reboot.
2. Pressing <command+s> to enter single user mode.
3. mount -o update /
4. vim /etc/sudoers X-D no of course I mean visudo.

Note: this is for OS X, and if you're using Linux, use your recovery disk and mount your /dev/sdaX.