When using a rocket and it passes through a lave block (source or flowing) it causes the server to kick everyone out
1. Make a firework
2. Spawn Lava (can be hanging above the block using the sign to hold lava back)
3. Use firework either in dispenser or on the block bellow the lava
4. Get kicked out of server

This is the same in survival and creative have only tested on servers
This doesn't work on Singleplayer