How to Block Facebook Invitations
Facebook invitations are a way for other users on the site to ask you to join a third-party application or attend an upcoming event. If a friend is overusing the invitation services on Facebook, block her from sending you invitations in the future. Your Facebook friends are never notified when you've blocked them, and you are allowed to add as many friends to your block list as you would like.
Click on the "Account" link in the right corner of the Facebook banner, which runs horizontally along the top of every screen on Facebook. Choose "Privacy Settings" from the drop-down menu.
Scroll down to the bottom of the screen and click the "Edit your lists" link in the "Block Lists" group.
Enter the name of a friend in the "Type the name of a friend" field in the "Block app invites" or "Block event invites" section -- as you type. Facebook lists friends that match your entry and clicking on a name once selects it. Blocking app invites stops other Facebook members from asking you to engage with them in third-party applications, such as playing games or taking quizzes. Blocking a friend from sending an event invite means that she can no longer send you an invitation to an upcoming party that she is organizing with the "Events" feature on Facebook.