Can place blocks into own head if block is placed onto a fence post (will test to see if it is possible with other blocks)
To recreate;
Make a 3x1 pillar, then destroy the bottom two blocks, stand under the one block* and look up and place a block. If it's a transparent block you can continue to stand there like it's nothing, if it's a solid block it will cause suffocation damage and push you out.
*The block must be a fence post (as of the time posting this, I've been unable to find another block allowing you to do this)