h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

For a great movie example of this sensitive topic see 'There's something about Mary'.
Personal experience (once done never ever forgotten) involved not moving a muscle and considering the situation. To move the zip down and therefore back open caused excruciating pain. Finally the solution bizarrely enough was to continue zipping upwards.

I've only just discovered this conversation - but it brings back painful memories. I was 13, my parents had treated me to my first pair of jeans, and they had the "heavy duty" type of metal zip - super chunky.
I took half an hour to lower the zip after the accident. 16 years later, and I still have a 1cm long scar to prove my carelessness.
My advice? As you zip, hold the thumb of the "zipping" hand inside the zip - this clears any object out harms way as the zip moves up.
To those who have never experienced this pain - think yourselves lucky!
To those who have, you have my sincerest sympathy!