Although you've been looking forward to your date for the last few days, sometimes things don't turn out quite as expected! In this case what does one do? When you're sitting there with him you realize that this is not what you were looking forward to, but you don't know how to end the date.
You've just been together for a short half hour and it seem that hours have passed! How come this happened so quickly? Well, there are quite a few reasons this could happen, obvious ones are bad hygiene or bad breath. The problem is he might not know, so you may either offer him a chewing gum and wait for the end of the date or make up an excuse that you're not feeling well and run home quickly.
These are of course drastic cases, usually you will need sometime to get to know someone. But do not feel compelled to go through with something that doesn't feel right, it won't help either of you.
If you really don't feel up to continuing with your date, you can for example end it between activities. If you're out on a bicycle or trekking for example, when you've finished you can let your date know that you're tired and will call it a day. It's a good idea to organize your first date planning activities, for you can always find an excuse if you see things aren't going smoothly.
Generally it's better to be honest with your date, if you see that the date isn't going well for you, the same is probably happening to the other person. He may feel that telling the truth is a little abrupt, but he'll respect you more so for being frank.
Although in extreme cases you simply can't find a better excuse than faking an illness, try and avoid this for your date will probably 'see' through your ruse and will be more hurt than if you told him straight out. Added to the fact that if it is not clear to him, he may try and contact you again.
Remember that whether or not your date went smoothly, do not forget to thank him. Make it clear that you appreciated the chance to get to know him and that you're sorry this didn't work out. This could be a good excuse to end the date early and avoid having to go through the whole evening.
Always remember that directness is the best approach, unless your date is really a creep respect the other person who is probably in the same situation as you are.