Lessons learned the hard way (idea)

• Why You Should Keep Your Contact Lenses Clean
  The thrilling tale of how one young person learned what happens if you take the easy way out of ocular hygiene
• How I nearly killed myself masturbating
  The gripping story of lust, danger, and bathtubs
• I got pierced
  *wince*
• Why you shouldn't ping-flood your printer
  Think that sounds fun? THINK AGAIN.
• Things you really shouldn't apply to your genitals whilst masturbating and Why Masturbating with Icy Hot is a Bad Idea
  Print these out and tape them to your porno collection. Or Icy Hot.
• duct tape does not make a good bra
  yowch. I thought it hurt the time I got masking tape in my hair...
• Caffeinated Nasal Spray
  You may laugh, but I considered this once... and then I read this.
• Bad things with which to wipe your ass
  
• Grapefruit Moonshine Beer Explosion
  You'd think that it's common sense, but no...

• Trust your hunches

There's also The Bad Idea Metanode, if you can't get enough bad ideas here.
More as I find them...