rollin:
So I believe it may in fact be an American idiomatic expression that has now found its way into our lexicon.
Translation: "On the bare."(a spanking on the bare bottom) would be a phrase having a special meaning not clear from the usual meaning of the words used in that phrase, and has become a specialized vocabulary for the spanko community.
As Rollin pointed out, "on the bare" has a special meaning in spanko lit; and I would vote to keep it. My favorite use of the phrase would be some thing like:
She found herself blinking at the floor, wondering how she got face down across his lap so fast with her skirt bunched up to her waist.
"OH! Please! Not on the bare!" she pleaded, as she felt her panties being pull down over her hips.
"Yes! On the bare." he said with a firm heavy SMACK to her up turned bare bottom.