You could just say you don't like the idea of dating someone you don't know. Personally, I don't like the idea of forcefully setting someone up. Just because you're a guy that doesn't want to date a female doesn't mean you're gay, and just being male doesn't mean you're easy to get with either.
If you actually do know her, just let her know you aren't interested. If she gets mad/upset she probably wasn't worth dating anyway (the same goes for guys who get upset at girls who put them in the "friendzone").