To invite all your friends to an event on Facebook without having to click every single friend one by one, follow this simple procedure:
1. Click invite friends on the event page.
2. Check all your friends are listed in the box. (you may have to wait a second before they all appear so you can select them all. if they don’t all appear go ahead but you may have to repeat the procedure.)
3. Copy and paste the following into your address bar and press enter:
All your friends will now be selected.
4. Click the Submit button. And you’re done.
Update: my or may not work in Google Chrome.