Be Nice or Be a Biotch?

Suppose you're on a date, and you've figured out pretty quickly (or maybe even not that quickly) that it's not going anywhere. Not that you're not having a good time, or the person isn't fun, nice, or cool... you just know there are differences that would not result in a second date.

I've been in this position twice recently. With both men, I had a great time. We went out, ate, drank, and enjoyed good conversation. However, about halfway through the dates, I knew I had no interest in going out on a second date. My question is, should I be nice and have fun, or turn into a bitch to avoid any awkward "follow-up" calls? Maybe I should just set it straight at the end of the date, when we part our own ways? This is difficult, because I am a genuinely nice person, and if I'm having a fun time, I'm going to show it. However, I've always had problems with men in my life (even generally speaking) confusing my niceness for being "sexually/relationship-wise" interested in them.

What to do?

*Ashley*