I found some tips from Cosmopolitan Magazine on how to bail on a bad date. Lets face it, we've all been there.  It's nice to have an escape plan.

First, if it is instantly obvious things are tanking, tell your date you got an urgent phone call as you were walking out the door to meet him and can only stay for one drink.

Next, if things take a sudden severe turn for the worse-and half the night is still ahead of you, shorten the date by inventing a morning appointment or huge work project that prevents you from staying long.

And Lastly, if it is obvious things are not going well, then be blunt.  Say, "listen, I've enjoyed meeting you, but I don't think we're clicking".

I hope that helps.