History: Believed to be a Gallagher-ism (American comic of 1980s & 1990s known mostly for pulverizing melons w/a huge slegehammer in his shows).
Definition: Those wisp-thin, slightly waxy paper toilet seat covers offered in public toilets to protect one's bodunkadunk from coming in contact with someone else's funk.
Also called a Texas t-shirt or a Portagee pegnoir.
This expression was common in the 1950s, and long time before the Gallagher was born. It's probably much older than that.