I have spent a great deal of time thinking about humor, and I've arrived at a place somewhat close to yours. Humor is how we pass on lessons about status and fitness, and we do that using pattern recognition. I heard a comedian describe comedy by saying, "It's always funny when someone falls down. The question is, is it still funny if you push them?" He said for a smaller group of the population, it is. Every joke has a person being displayed as not fit - even if we have to take an object, or an abstraction, and anthropomorphize it. This is the butt of the joke. The more butts of a joke there are, the funnier the joke is - i.e., a single butt will not be that funny, but if there are several butts of a joke, or if a single person is the butt of several layers of the joke, it will be seen as funnier. The most common form of this is when the goals of the butt of a joke is divorced from their results.

Joke 1: This is funny because Jeremy displays a lack of fitness by not being able to properly process the phrase "on TV." This has one butt - Jeremy.

Joke 2: This joke has two butts. One is the muffin, which is being declared unfit for being bald. The other is the comedian's character, who is being displayed as needlessly paranoid toward a benign object (a muffin).

Joke 3: This joke isn't that funny when displayed in text form - the comedy is in the performances, where both conversation participants are butts of the joke for arguing so intensely over something so petty.

Joke 4: The butt of this joke is the traditional joke it's mocking.

As for your outsiders' behavior:

New student asks for both cream and lemon: Displays he is unfit by not understanding the purpose of what he's asking for.

New employee swears and makes racist comments: This isn't funny in person, but it is funny if a few conditions are met. The first condition is that you're sufficiently removed from it (i.e., watching it on TV): Imminent threats aren't funny because this isn't a status lesson, but a status competition. The second condition is that it must be demonstrated how this makes the person unfit. For example, if the new employee is making these comments because she thinks they demonstrate her social savvy, that starts becoming more funny again (notice Michael Scott in The Office). Or, imagine the new employee has Tourette syndrome and is actually a very sweet girl, who constantly apologizes after making obscene statements. This also would elicit laughs.

If the guy sitting behind you starts grunting and moaning: The threat is too imminent, but if you remove the worrying aspect of it, this is ripe for a punchline. Once again, you have to demonstrate how he is unfit. Perhaps he says, "I'm trying to communicate secretly in Morse Code - grunts are dots, moans are dashes."

EDIT / ADDENDUM: This also explains why humor is so tied up in culture - you don't know the purpose of certain cultural habits. Until you intuitively grasp their purpose, you will have a hard time understanding why certain violations of them are funny.

For example, take the Simpsons episode where Homer's pet lobster dies and he's weeping as he eats it. In between bouts of loud, wailing grief, he sobs out comments like, "Pass the salt." This would be hard to understand for cultures that don't express grief like Western culture does.