Unfortunately, humour is not my forte, so don't expect anything special on this page, however I can tell you the structure of a joke that nobody will find funny except the person telling it. Beware that you should not use this unless you are either with weak people, or don't mind being hit copiously. One of my friends uses this method, and I have picked up the annoying habit of doing so too.
Firstly, you pick a bizarre topic (for the sake of this explanation I shall use the example of "the alien joke") such as green aliens visiting your local town, and a big red alien that likes to eat these green aliens.
Then you waffle, or make the joke as long as you possibly can. In my example, you can start of with a ridiculously large number of green aliens, so that even when it gets halved each time, it still takes 30 minutes to reach 2 aliens.
After deciding on your material, you make up a stupid story. In my example, the green aliens visit a hotel in the area on holiday, only hiring out two rooms, the red alien eats all the green aliens in one room except for one who runs and tells the others, who go back to their planet. This continues until there are only two left.
For the full effect of the joke, you MUST make it last ridiculously long, and make sure nobody has an idea of the punchline.
Speaking of the punchline, you must now think up a totally unrelated moral. In my example, "the moral of the story is to always make sure you have a good bike".
You then must find a way to link the story and the moral together. In my example, one of the final two green aliens is intelligent, and makes himself a good bike, so that when the red alien comes down the next time, he is able to escape.
As you can see, this joke is not in the slightest bit funny, and is a complete waste of time which is what makes it so fun to tell, especially to drunk people, half an hour before the bar closes. The expressions on peoples faces should be favorable and you can be proud to dubb yourself the worst comedian in history.