Will-o’-the-Wisp

http://en.wikipedia.org/wiki/Will-o%27-the-wisp
A will-o’-the-wisp or ignis fatuus (Latin, from ignis, “fire” + fatuus, “foolish”), also called will-o’-wisp, corpse candle, jack-o’-lantern, friar’s lantern, gunderslislik, and wisp, is a Folklore depiction of ghostly light sometimes seen at night or twilight over bogs, swamps, and marshes.
“Ignis fatuus” is one of those wonderful phrases that sounds like it should be an insult, but isn’t.
Reminds me of the time one of my white trash cousins called the other an “oxymoron.” We all laughed…but I stopped when I realized he was serious.