To do a bat party, follow these steps:
1. Go into an enclosed space.
2. Hold a bat spawn egg. (At least 30 in survival mode and 1 in creative mode)
3. Click the ceiling repeatedly on one spot.
4. Hit the "bat wheel", as I call it.
5. Watch the bats fly away, initiating the Bat Party.

This screenshot was taken in an NPC village, but whatever! It's still an enclosed space.