Dear 100 Hour Board,
I went on a date with a guy and, while we had fun, am not really interested in a second date. He asked me on one. Is going on a second date the polite thing to do, or is it okay to tell him that I think he's awesome but don't really want a second date?
If you're one of those people that sometimes changes their mind about not wanting to date someone after two or three dates, you should go on another date with him. If you aren't, I would definitely rather not go on a date with a girl that had already decided that she didn't want to date me. It's actually a lot more polite and considerate of his time and his feelings to tell him that you don't want to go on another date with him.
I just hope you didn't make him wait 100+ hours for a response after he asked you out.
I'm with Ento, if you're already certain that you're not interested, then declining the second date is really the most polite thing to do. To say yes would have communicated that you're still somewhat interested. And in my opinion/personal experience, honesty is always gonna be your best policy.
Keep it real,
Going with the above writers here. I'll re-hit Ento's point about sometimes it's possible to like somebody more after a second date, so being open to possibilities is good and shutting people down prematurely can be harmful, but if your mind is really made up, it's fine to reject a second date. Not only will he likely appreciate the forthrightness, it'll save you an awkward date.
(You didn't ask for this, but if you're looking for mechanics on saying no, I wrote this one a while ago.)