What's in a joke

There's only a few people on here, but let's get busy anyway! I'll lay down first, starting with something near and dear.

Humor.

I find humor to be one of my most favorite subjects. Half the laughs come from making up the material. Which goes into my first question:

How do you (if at all) go about making a good joke? Do you take from other sources, repeat a popular gag, go with a solid style of joke?

I ask because I think a joke or any funny part in a story should be planned and taken as seriously as the rest of it. I don't like making charatcers act OOC for a cheap giggle. I like the slow build-up, then that moment where you finally "get it".

How bout you guys?

For me, it depends on the characters and setting of the story. I normally use their surroundings to make a joke. I also suit the joke to the person's age. I normally won't let the character make an actual joke (you know, like Hoagie's corny ones).

Well, to my knowledge, there are at least five ways of creating humor:
a) using a running gag. b) emphasizing a character's personality quirks. c) short-term surprises. d)long-term surprises (namely plot twists). e) putting characters in a really unfamiliar situation (for example, having Wally and Kuki switch bodies).
f) And lastly, having the character make an actual joke. I agree with you, CodeLyokoIsTheBest, it usually doesn't work. But it can be funny if done skillfully and if it involves a character renowned for making bad jokes (namely Hoagie).
There are probably more ideas, but these are the only ones I can think of right now.