I once picked up a girl on a train station, it was her day off work and she was going to the city to watch a movie with some of her friends. I asked her what she do for a living and it turns out she is a cop. Kind of freaky for me, dating a cop, not interest in the idea of dating a girl tougher then me. I got her number, but I never called her back.
So, one thing you should never say to a cop, is never ask her out on a date!!! (That is unless you are an e.g. cop, a soldier or a martial art expert.)