Eleven O'Clock Princess 

(used only in UK) - 1) A potential female sexual partner only chosen because it's eleven o'clock at night (last orders) and you still haven't pulled. 2) A not-too-pretty female who you wouldn't look twice at sober, but who takes on a princess-like aura by eleven o'clock, usually after you've had a number of drinks.

"Look at her! She is gorgeous!"
"Nah you pisshead. She's just an eleven o'clock princess"

Eleven O'Clock Princess by Marc GJ May 19, 2004