The Irritation Trap

This trap is an anti everyone trap.It's also very irritating.

Build a 3 by 3 square with pressure plated on the outer blocks.Leave a space in the middle.

Place a piston next to each of the planks.

Place 3 blocks in the centre going up.Then place slabs all around those.

Destroy the 3 blocks and replace the top one with a slab.
Now when you walk in, there's no way out.Congratulations!