1. Try on the Batman costume
  2. Spend the entire weekend speaking in the "Batman voice"
  3. Use the Batcomputer to download porn.
  4. Practice sweet slides down the Batpole.
  5. Ring the butler bell, then when Alfred comes, say "never mind." Repeat
  6. Throw a massive keg party, that turns into a rave and takes over the neighborhood, goes joyriding in the batmobile and forgets where he parked it the next morning only to find it wrapped around the telephone pole in front of the entrance to the batcave. Man, what a party!
    Suggested by @gilbaron
  7. Replace the generic computer voice with the voice of Groot
    Suggested by @p
  8. Set all batclocks 10 minutes into the future
    Suggested by @p