'Arousal Faucet'
Context: 'Yeah, she's an arousal faucet -she was arousing once, but is now, for whatever reason, not arousing anymore. On and off, just like a faucet'.
Examples:
Heidi Klum (maybe? I dunno, she's in good nick)
Lindsay Lohan
Britney Spears
Shannon Doherty (remember that chick from the 90s?)
Hilary Duff
Selena Gomez