Back in the middle ages, a popular form of torture is to force a poor sap to sit on a pointy stool called the Judas Cradle. You can imagine what that does to the guy's backside.
Fast forward to modern times and lo, this torture chair was transformed into an edgy "Stake-chair" by Russian designer Ton Guglya:
Stake-chair and stake-stool for those who like to be «on the edge». Practically it is very comfortable to seat on a glass cube (with round corners and a deepening in the top). Woody structure is actually wooden. If you doubt the historical authenticity of the torture stake — search it on the internet.
http://www.coroflot.com/public/individual_file.asp?individual_id=189064&portfolio_id=2307757& - via a+.29