Wow! What a great question; I love tracing down crazy expressions. :)
This was a tough one but here it is:

"The root of this stems from the form of torture used by the British, on the Irish. When a person was suspected of having information that they considered valuable, and that person was reluctant to talk, the British, during the Irish Rising of 1798, employed what they called "Pitch Capping". A hat or cap was filled with hot liquid tar and then crammed onto the hapless victim's head. When the mass had cooled, it was removed, along with the victim's hair and scalp, by snatching it off his head from the rear forward. Pitch Capping was also employed by the British on the American colonists during the Revolutionary War."

http://freepages.genealogy.rootsweb.ancestry.com...

I've never heard that saying before, so I'll change it to "I'm going to make your snatch bald." :-P

Positroll attack...+100.