Scratching wildly at eczema on the back of your knee for five minutes.
Benefit: Unrelenting pleasure for five minutes.
Drawback: Unrelenting owie for five hours.
( Hoohah Bibbly-bobbly-bubbly-snibbly wib-wib floppit., Fri 12 Jan 2007, 23:26, archived)

You've spelt it wrong.
It's "exmah".
( rnuk http://flickr.com/rnuk, Fri 12 Jan 2007, 23:34, archived)