I have never used a 'chat-up line', but I wrote a monthly feature for a magazine that involved interviewing about sixty people in an evening in various night-clubs, and one of the questions was the worst chat-up line you've used - heard?
Best was - "Do you like group sex? No, nor me, just the two of us then?"
Worst was - "Do you come her often?" - apparently guys do still say that!
The best one I know, but would never dream of using, even when single, is
"I have to know your name, because otherwise, when I dream of you tonight, i can only call you 'Baby'."