I've been comedy obsessed my entire life and love studying stuff like this - so if you've got your own examples, I'd be thrilled to hear them.
  1. The cartoon character that doesn't realize he's run off the edge of the cliff and is able to levitate - then slowly realizes what's happened, feels around the air for a beat, panics, tries to run back to the cliff and instead plummets to the ground.
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    An amazing, Zen metaphor for denial and consciousness.
  2. Characters in "gross-out" comedies unknowingly ingesting semen or shit, or smearing it all over themselves (hair gel in There's Something About Mary; "nutty" coffee in Austin Powers; semen-filled pastries in Van Wilder; mud bath in this year's Vacation remake; etc.).
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    "In every fear, a secret wish." The transgressive impulse made forgivable by "obliviousness"; if the characters were aware of what they were doing, it would come too close to acknowledging that this is audience wish fulfillment.
  3. Racial "humor," based in stereotypes - ALL of which are actually characteristics of the person making the joke, projected onto an "other."
    Because they're too ashamed/ afraid to acknowledge that the stereotype is actually a description of their most deeply held self-beliefs. But they get the catharsis of playing out this "true self," AND the power rush of victimizing the "other."
  4. Vapor trail coming from the steam of a freshly-cooked pie, which wafts over to a cartoon character like a beckoning finger, then lifts him in a trance toward the pie.
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    Sensory overload/ intoxication/ powerlessness/ addiction process.
  5. Abbott and Costello "misunderstanding" bits like "Who's On First" and (especially) "The Restaurant."
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    The most primal experience of inability to achieve human connection, between a "child" without a strong-enough grasp of language (Costello), and a frustrated, angry, punishing "father" (Abbott).
  6. Overplaying the literal
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    Statler - "it wasn't half bad" Waldorf - "it wasn't half good either." Reminds us of the elasticity of language and meaning, and how figurative language often takes meaning beyond the words themselves.
    Suggested by @gilbaron