Placing a boat on top of a slime block and then getting in it will launch the player and boat in the sky.

If any of the boats is placed on a slime block, a player who gets in it will get launched in the air. Once the player gets out of the boat, it will fall back down and break. How long the boat has sat on top of the slime block affects how far it will be launched when the player gets in it. If the boat launches more than 150 blocks and the player has not yet gotten out, the game will crash.