Back when I were a wee nipper (like 10 or something) I had to have one of my baby teeth pulled cos it wasn't falling out as the new tooth was coming through so the nerve in it had died and gone all manky and stuff...
...so had the injection (hurt a bit) and then they just whipped out the pliers (i'm sure there's a technical dentistry name for them, but they were pliers) and yanked and i could feel the vibrations of it cracking and stuff, which made me cringe even though it didn't hurt. Having a numb face is cool though.
On a slightly worse note, one of my mates at uni was telling me her dad needed a tooth pulled, and when they came to do the injection they managed to ram the needle right into the nerve of his tooth and injected right onto it - needless to say much swearing followed this, as it's apparently one of the most painful things ever. I guess if you imagine acute toothache and then imagine someone poking the inside of the tooth with a sharp object, you could get close.