April Fools 2012 is a new mission, which requires 225 LOLs (from the Comedy Club) and 1350 Trick Shots (from the Billiard Hall).
Once you tap this mission, you should be given the option to Decline or Accept. If this isn't working for you, try resetting the game by removing it from your currently running apps.
If that doesn't work, be sure that your Tiny Tower is the latest version (v1.5.2 for iPhone).
