To get rid of endless Facebook invites to play "Candy Crush Saga" just unfriend the person who started the invite.

If you friend them anew, you will be on the other side of the problem. Your friend does not realize they are spamming you.

Addendum 12/26/2013: I have spoken too soon. I had a window of quiet and then now, today, I've gotten a new request. Boo. I may need to REALLY unfriend Nichole FOREVER.