Broken spark plug boot...
 

Created my first Instructable fer making yer own inexpensive broken boot removal tool...
Making An Inexpensive Broken Spark Plug Boot Removal Tool

Costs about $3 and will remove that stuck boot in a few seconds. Nothing else like it. You won't need something like this until you need it. ;)

Got my first reply to my Instructable! Guess my invention is doing someone some good. ;)

I'll be making one of these... or several, if different lengths / shapes can help access different plugs better. I don't know if many people would ever really need one, but I imagine I'll be very happy to have it in the toolbox at least once per 10 - 20 vehicles I put plugs in.

I actually keep the one I made fer the Instructable in my glove box. Haven't had the opportunity to use it just yet but I know I don't want to struggle with a broken spark plug boot ever again if I have to work on someone's spark plugs again. ;)