For OSX, open Terminal and run:
$ open -a Google\ Chrome --args --disable-web-security
For Linux run:
$ google-chrome --disable-web-security
Also if you're trying to access local files for dev purposes like AJAX or JSON, you can use this flag too.
-–allow-file-access-from-files
For PC go into the command prompt and go into the folder where Chrome.exe is and type
chrome.exe --disable-web-security
That should disable the same origin policy and allow you to access local files. Update: For Chrome 22+ you will be presented with an error message that says:
You are using an unsupported command-line flag: --disable-web-security. Stability and security will suffer. However you can just ignore that message while developing.