This is an old, old cartoon parodying the way ancient yogis might have fashioned their bathroom. Of course, there’s nothing mystical about a bed of nails. It all has to do with evenly distributed weight and just being damn careful.
I originally drew this cartoon in my late teens and then redrew it later around the year 2000 to post on the web. It’s one of those cartoon ideas that has persisted because it so simple and so ridiculous to imagine. If you were to design a real bed of nails toilet seat the nails would be much shorter. I don’t know if the concept would be possible because sitting down may not balance out your weight and those nails could start digging in to some plump cheeks.