What To Do For A Friend's 50th Birthday?

2 ideas....depends on how much time you have before the party.  

1) declare it to be (the guest of honor's name) Day.  Have friends come dressed as their best/worst interpretation of the honoree.  Find a good photo, blow it up and create face masks of the honoree for guests to hold for photos and as the honoree arrives.

2)"The Blackmail Ball"  Mail funny photographs of the honoree with the invitations, asking the guests to tell a funny  or outlandish (maybe true, maybe not) story about the guest of honor.  Decorate with photographs/photo collages of the guest of honor.  In 50 years....there can be a lot of crazy stories!